Copyrights and Credits

Prologue…or Epilogue

Prologue...or Epilogue

THE GUINNESS CASCADE is a phenomenon associated with a dark, near-black Irish dry stout called Guinness. Here in Japan, you rarely see that beer in stores, but in its country of origin, they drink it so often that it’s referred to as “a meal in a glass.”

When Guinness is poured into a wide-rim glass, you can see the pale bubbles sink inside the dark brown beer until the two finish separating. But wait a minute, you say, isn’t it impossible for gas to sink in a liquid? No, not quite—and there’s a very simple explanation.

Due to the viscosity of the beer, when the bubbles rise, the liquid within close proximity is pushed up along with them. But because its density is greater than that of the bubbles, that liquid is then pushed out to the edges, and a vortex is created within the widest part of the glass as the beer subsequently pushes the bubbles back down. And so, the bubbles “cascade” with the beer along the sides—then rise again at the center of the glass, where you can’t see it.

This is nothing to brag about, but as a guy who drank his fair share of alcohol when he was younger, I saw the phenomenon with my own eyes several times. It wasn’t until I was pushing forty, however, that I learned it was called a Guinness Cascade.

The story itself is nothing special. I just happened to be at a bar, and I just happened to order a Guinness. Then I saw the bubble effect, and I just had to ask the bartender about it.

Why was I in such a rush, you ask? Because at that exact moment, I was looking for something with the power to turn my whole world upside-down—and wouldn’t you know, the concept of “sinking bubbles” did just that.

Bubbles can sink.

With that inspiration, I devoted the rest of my life to making it happen. I needed the viscosity of the beer to surpass the bubbles’ buoyancy. Then I could create a downdraft.

Bubbles can sink.

By opening my eyes to this concept, that single pint of beer was worth its weight in gold to me. And sure enough, about ten years later, I found a way to make it work. I just needed a time and place to sink them—so I spent another twenty years after that carefully setting it all up. And by the time I arranged the perfect spot, I was well past seventy.

I had lived for so long. Too long. And for what? I had no wife, no children… What even was my life’s purpose? Because of me, the one person I ever loved was wiped from the face of the earth.

But, well, at least it was almost over.

Bubbles can sink.

At last, the time had come to do away with this world once and for all. Because to me, a world without her in it was as good as worthless.

Chapter 1: Childhood

Chapter 1:
Childhood

AT AGE SEVEN, I understood what “divorce” was, and when my parents asked me to choose one of them to live with, I didn’t throw a fit.

My father was a celebrated researcher in his field while my mother came from a wealthy family. No matter who I chose, I would have all the financial security I needed, so I was free to let my heart decide—and ultimately, I chose my father. Not because I loved him more than my mother, but because I was afraid she wouldn’t be able to get remarried if I was around.

The root cause of their divorce was poor communication. My father spent many a night at his laboratory, and whenever he came home, he would tell my mother all about his work. Naturally, to her, it was total gibberish. Alas, my father was the kind of man who automatically assumed everyone else understood all the same things he did, and I often watched my mother struggle in conversations with him while he remained blissfully unaware.

Therefore, based on their personalities, I decided Dad was less likely to get remarried. Well, no—I’m sure my thought process at age seven wasn’t quite that clear-cut, but you get the point.

Ironically, the divorce dramatically improved my parents’ relationship, and they cheerfully traded me back and forth at least once a month. Obviously, they had to have loved each other very much considering they got married and had a child in the first place, but it was clear this degree of separation was healthy for them. Personally, I was just happy that they stopped fighting and relieved that it wasn’t because of me.

Once it was just me and Dad, I started popping into his workplace. After school let out, I’d go to his laboratory and wait for him to finish his work so the two of us could go home together. The lab was open seven days a week with rotating shifts, so whenever he had to work on a weekend, I just spent the whole day there.

As part of its benefits package, the lab allowed its employees to leave their young children in the onsite daycare room. It wasn’t a fully-fledged daycare with its own staff or anything—it was just a room where employees took turns babysitting us. As the oldest, I helped look after the little kids, and the busy grown-ups thanked me for it.

Whenever there were no other kids in the room, which was often, I would spend my time reading through the books on the shelves. Instead of picture books, they kept dissertations and scholarly works pertaining to my father’s research. Naturally, I didn’t understand a word of it at first, but some of the books were written in a “For Dummies” way with lots of illustrations, and I managed to power my way through those. The discovery of the unknown made my heart race.

Dad must have been pleased that I was developing an interest in his work. He often came by during his breaks to check on me, answer my questions, and explain his research through simple analogies even a kid could understand.

One day, he pointed at a big tank full of tropical fish. “These bubbles represent the world where you and I live,” he explained.

Unlike my mother, he didn’t refer to himself as “Daddy” when speaking to me, and once it was just the two of us, I stopped using that word myself.

In the tank, I could see big bubbles rising from the aerator pump.

“See how the bubbles get bigger and bigger? Held at a constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure. This is called Boyle’s law, and—”

“Wait, I don’t get it. What’s ‘inversely proportional’?” I asked.

“You haven’t learned about proportionality in school? When do they teach that?”

“I don’t know, but not yet. Give me an analogy.”

“Hmmm… Okay, let’s say a candy bar is 100 yen. If you buy two, they’ll cost 200 yen, and if you buy three, your total’s 300 yen, right? When both values go up in relation to each other, that’s called directly proportional.”

“Okay.”

“Now, inversely proportional is the opposite of that. If you split six candy bars between two people, each person gets three, right? Split it between three people, and each gets two; between six, and each person gets one. When one value goes up while the other goes down, that’s inversely proportional.”

Dad would always default to using big words, but if I told him I didn’t get it, he would do his best to rephrase it more simply. If only Mom had admitted to her lack of understanding the same way I did, maybe they could have stayed together.

“The deeper underwater you go, the higher the pressure is—that’s the force pushing against you. This means a bubble’s volume—size—goes down the deeper you go. As these bubbles travel upwards, the pressure gets weaker, so they get bigger. That means their volume is inversely proportional to their pressure, which is what we call Boyle’s law.”

“Boyle’s law?”

“Yes, Boyle’s law.”

“Got it.”

“Very good!” he said, praising me.

Satisfied with my response, Dad went back to pointing at the bubbles in the fish tank. Apparently, he had more to teach me.

“In my field, we theorize that our world is like these bubbles, so we’re testing to see if information can be exchanged from one ‘bubble’ to another.”

I remembered him comparing our world to the bubbles at the start of our conversation, but what did it mean?

“See, our world started as a tiny bubble born on the ocean floor. Over time, it floated up, growing in size—and along the way, it split in two. We’re in one of them.”

“What about the other one?”

“We’re in that one too, but it’s not the same as this one. Maybe in that bubble you went to live with Mom instead.”

There’s another me that chose to go with Mom?

“We refer to these other bubbles as parallel worlds,” my father explained.

“Parallel worlds?”

“Yes, parallel worlds.”

“Got it.”

“Wonderful!”

Truth be told, I didn’t grasp this concept quite as well as the analogy about direct and inverse proportionality, but I did my best to soak up knowledge like a sponge. As a result, I never struggled with schoolwork because I was always learning things years ahead of my peers.

“We believe that human beings subconsciously travel between nearby bubbles on a daily basis. The closer a bubble is, the fewer distinctions there are between them, so it’s possible most people simply never notice anything’s different. If that’s so, we first want to prove it. Then, our aim is to control it. This is what our director calls the study of imaginary science.”

At the time, I didn’t fully grasp just how incredible that was. I was a smart kid, sure, but I was still in elementary school. My only real reaction was, “Wow, neat.”

But a few years later, as I was turning ten, that ignorance proved dangerous.

***

“Koyomi?”

After a phone call, Dad called for me in an uncharacteristically grave voice. Part of me was annoyed that he was interrupting my video game, but he sounded so morose that I couldn’t possibly ignore it.

Sure enough, when I glanced over, he was standing there, looking devastated. I’d never seen him so sad before… What in the world was that phone call about?

“I’m told Yuno passed away.”

“…What?” I asked.

Yuno was the name of the dog that lived with Mom at my maternal grandparents’ house. She was a golden retriever, and despite being bigger than me, she was a total needy baby. Whenever I went over to their house, she’d jump up to greet me with her tail wagging up a storm.

But now…she’s dead?

It was so sudden that I couldn’t process it. I squished mosquitoes and flies without hesitation, I ate meat, and in video games I killed monsters all the time. But Yuno wasn’t a bug, or a monster, or food. How could she die? Though I was old enough to know better, some small part of me wondered if I could revive her with magic or an item.

“How did it happen?”

“A neighbor’s kid ran out into traffic and almost got hit by a car, but Yuno jumped out in front… She died a hero.”

I was the one who asked for this information, but I found myself rejecting it regardless. What was I supposed to do with it? How was I supposed to feel?

“I’m told that they dug a grave in the yard at your mom’s place. Wanna head over?”

“Uhhh… I’m in the middle of my game,” I answered reflexively, even though I knew this was way more important.

“…Okay. Some other time then.”

I thought he would yell at me for having my priorities wrong, but instead, he looked at me with sympathy.

Somehow, for me, that was a thousand times worse.

“On second thought, let’s go right now,” I said while shutting my game off. I got dressed, we hopped into Dad’s car, and together we drove to Mom’s house.

It wasn’t far from our place—only ten minutes by car, and close enough for me to bike over whenever I wanted. In fact, in the early days of their divorce, I used to go there all the time—partly to see Mom and Yuno, of course, but also my grandpa. He was a nice guy who gave me a piece of candy every time I visited. Over time, however, I started visiting less and less… In fact, this year, I hadn’t been over since New Year’s.

“Oh, Koyomi, you’re here. Come with Mommy.”

I hadn’t seen Mom in months, and she looked alarmingly distraught about the loss of Yuno. It was so alarming that I started to worry if I looked that distraught myself.

“You okay?” Dad asked her.

“Yes, thank you,” she replied with a small, relieved smile. I was happy to see the two of them getting along, circumstances notwithstanding.

Yuno’s grave was located in an empty corner of the backyard. There, the earth was raised only slightly, and it was hard to believe that the family dog was buried there. If anything, it seemed cruel to trap her down there all alone.

“You know, Grandpa adopted Yuno around the same time you were born, Koyomi.”

That was a story I’d heard countless times before, along with a famous poem that I could practically recite offhand.

When you have a child, get a dog.

In infancy, a guardian;

In childhood, a playmate;

In adolescence, a shoulder to cry on;

And in adulthood, with its death, the value of a life.

If this poem was true, then Yuno died way too early. I was only nine years old still. Maybe that was why I couldn’t feel “the value of a life” while staring down at this grave.

“Sweetheart, why don’t you go inside and say hello to Grandma and Grandpa?”

And so, at my mother’s prompting, I walked off into the house.

“Koyomi, my boy! Welcome. Thank you for coming.” In the months since I’d seen him, my grandpa appeared to have aged tenfold. He was the one who adopted Yuno, so maybe her death hit him the hardest.

He later invited me to spend the night, but I declined. Something in my gut told me I needed to actually grieve Yuno’s death before I could spend any more time with him.

***

A month or so later, I had all but forgotten about Yuno. I still felt guilty that her death hadn’t made me sad, and that kept me from going back to Mom’s house.

On that particular day, I was hanging out at the lab daycare like always. No one else was there, and I was bored of reading the same old books, so I decided to turn the TV on. But as I was flipping through channels, I suddenly stopped. There, on-screen, was a big golden retriever who looked just like Yuno. Before I knew it, I was invested.

It was a news feature about dogs who helped people in different ways. A seeing-eye dog aiding its blind owner, a search-and-rescue dog finding survivors after a natural disaster, a sea dog towing a boat back to shore with a rope in its teeth, a loyal dog waiting endlessly for an owner that would never return, a Soviet space dog who was sent on a test flight… With tears in his eyes, the news anchor praised the courage of each and every one of them, speaking passionately about “man’s best friend.”

And as I watched the show, I found myself growing more and more furious.

What was I angry at? I wasn’t sure. Heck, I wasn’t even sure what I was feeling was really anger at all. Maybe I was just bitter. But if so, why?

With no answers to help me, my eyes grew hot. I didn’t even know why I was crying.

“What’s wrong?”

At the sudden voice, I looked up in surprise. I thought I was alone in here, but the next thing I knew, I was joined by a pretty girl with long, straight black hair cascading over her white dress. She looked to be about my age. Was she some researcher’s daughter? I had never seen her here before.

“You’re crying. Are you hurt somewhere?” she asked as she walked up to me with concern on her face.

I was embarrassed to be caught crying in front of a girl, so I wiped my eyes roughly with my sleeve. “I’m not crying.”

“Yes, you are! What’s wrong?”

“I’m not!”

Annoyed by her persistence, I glared at her. But…for some reason, those clear, innocent eyes reminded me of hers…

“I just…want to see Yuno again,” I murmured unconsciously.

That was it. I wasn’t angry or bitter—I just missed my dog, and because I could never see her again… I was sad.

“Who’s Yuno?”

“My grandpa’s dog.”

“Why can’t you see it again?” she asked.

“Because she died.”

The instant those words left my lips, it finally sank in: Yuno was dead. Gone. And it made me so incredibly sad.

“She died… And I’ll never see her again…!”

Before I knew it, the dam had burst, and all the tears I never shed at her grave came flowing from my eyes. I cried so hard, it no longer mattered that a girl was watching. Nevertheless, to preserve the last dregs of my pride, I clenched my teeth to keep from sobbing audibly. That way, no one else would have to know I was crying. Sure, this girl may have been witnessing it, but…for some reason, I decided I could live with that.

She stood beside me the whole time, waiting for me to finish. And once I was calm again, she offered me a spotless white handkerchief.

“No thanks,” I said.

It felt like a crime to tarnish something so nice and clean, so I wiped my eyes with my sleeve again. She kept holding it out for a while, but I continued to ignore it. Eventually, she gave up and put it back in her pocket. Then, out of nowhere—

“Come with me.”

“Wha—?!”

She grabbed me by the arm and started running with me in tow.

Today was a Sunday, so there weren’t as many employees around. The few who did show up mostly left early. The whole building felt deserted in its silence…save for our footsteps as the girl led me down hallways and around corners.

“Hey! Where are you taking me?!”

“Be quiet or my mom will catch us!”

Was she waiting for her mom to finish work the same way I was waiting for my dad? Clearly, she spent a fair amount of time here if she knew her way around so well. Normally I did as I was told and never poked my nose anywhere it didn’t belong, but that didn’t mean I wasn’t interested in exploring. Where did this hallway lead? Or that door, or those stairs? It was that curiosity that compelled me to follow this girl’s lead.

At last, she arrived at a door and opened it. The sight of what was inside made my heart race.

“Wow… What is this place?!” I exclaimed.

At the center of the room sat something that looked like a cockpit from a mecha anime, connected to all sorts of cables. Sure enough, through the glass door, I could see that the interior was designed for a person to fit inside.

“Mom said if you climb inside this pod, you can visit parallel worlds,” the girl explained as she stroked the glass.

“What…?”

Parallel worlds? That was the same thing Dad was always talking about—how this world was a big bubble that split into two, and the other bubble was a parallel world to ours, complete with a parallel version of each one of us, living different lives…

“Don’t you want to see Yuno again?”

“Yeah…?”

“Well, maybe there’s a parallel world where she’s still alive!”

This was a tempting proposition. Her death had come out of nowhere, so I couldn’t even remember the last time I saw her. Did I play with her? Did I pet her? I had no recollection. So if I could see her one last time…

“…Okay, what do I need to do?”

“Get in.”

At her prompting, I opened the glass door and climbed into the pod. My heart began to race. All of a sudden, it felt like my life had turned into some kind of anime or video game.

Once the door closed behind me, I started to hear some clicking noises, so I sat up to investigate. Through the glass, I could see the girl standing at a console with tons of buttons, dials, and switches. It didn’t look like she knew how to operate this thing at all. As far as I could tell, she was fidgeting with them at random.

“Hey, are you sure you know what you’re doing?”

No answer. Instead, she kept on pressing, twisting, and flipping with a stern look on her face. What was she so stressed about? I somehow doubted anything she was doing over there was going to send me to Yuno.

“Do you need help?”

“I’m fine! You just lay there and focus!” she called out.

“On what?”

“I don’t know… Try praying or something, like, ‘I wanna be in a world where Yuno is still alive’!”

“Does that even count as praying?”

“My mom says the most important part is to believe. Only those who never stop believing have the power to change the world.”

I didn’t really get it. She kept going on and on about her mom, but I didn’t even know who her mom was. That said, she appeared to be dead serious about whatever she was doing at the console…so I decided I would try to pray.

Take me to another world. A world where Yuno is alive.

I thought about Yuno—the way she bounced around when she was alive. I thought about the small grave in the backyard, and the news feature about dogs who died helping humans. I thought about the way the commentary made me so inexplicably angry. At first I wasn’t really trying, but the more I thought about her, the more serious I became about seeing her again. So I closed my eyes and prayed even harder.

Take me to a world where Yuno is alive—!

***

—And there in front of me, my mother was crying.

“Huh?”

This was such a drastic change in scenery that my brain couldn’t keep up. The most I could do was focus on identifying everything I could see, one after another. My crying mother, the dining table, and…Grandma? Yeah, Grandma. Also crying.

I looked around. I was no longer inside the mecha cockpit, and instead was now in a room I recognized. Specifically, it was the living room at my mom’s house. I was last here a month ago when I came to visit Yuno’s grave. And I was very, very sure I wasn’t here a second ago.

So why was I here now? What happened to that girl? Or the pod I was in?

Oh, right.

That was when I remembered what I was doing—the whole reason I climbed into that pod to begin with. Could this be…?

“Hey, Mom?” I began timidly.

But just then, as if to answer the question I hadn’t yet asked, I heard a sound from outside. A very familiar bark.

I jumped to my feet and ran outside like a bat out of hell. And when I ran around to the backyard…

“Yuno…”

That was where I found her—the dog that was supposed to have died a month prior. But here she was. Alive.

“Yuno… Yuno!”

I ran up to her and threw my arms around her big, fuzzy body. When I petted her head, she jumped up on me with her tail wagging, just like usual.

I never thought it would work, but somehow it did. This was a parallel world—a world where someone who died was very much still alive. Did all that random switch-flipping actually send me here? Was it my prayers? Either way, I was unmistakably here. My prayers were granted, and I was reunited with Yuno one last time.

She rolled over onto her back, and as I gave her belly rubs, I stared down at her. In my world, she died, but here in front of me, she was alive. Here she was warm, but in my world, her body was cold and lifeless under the earth.

Then I remembered that poem Grandpa always recited to me. “When you have a child, get a dog… With its death, the value of a life.” Was the warmth I felt against my palm “the value of a life”? If so, then once I returned to my world and went back to Yuno’s grave, I’d probably understand it for real.

Fighting back tears, I showered her with lots of pets, then contemplated my next move. In my world, she died after being hit by a car. What if I warned Grandpa to keep her away from the road? Surely that was better than nothing. With this new objective, I went back inside the house.

In the living room, Mom and Grandma had stopped crying, but they still looked devastated. What in the world had happened to make them so upset? I wanted to ask, but it was too risky. If I asked a question my parallel self already knew the answer to, they’d get suspicious. I needed a safer question…

“Hey, Mom? What’s the plan for tomorrow?”

By my estimation, my mom would interpret this however she saw fit. And sure enough, my gamble paid off…mostly. Her answer contained a word I hadn’t learned yet.

“Tomorrow we’ll be holding a wake for Grandpa.”

“A wake? What’s that?”

“Well, when someone passes away…”

And that was how I learned that in this world, my grandpa had died. I could now count three major differences between this one and my own. Here, Yuno was alive, Grandpa was dead, and instead of my dad, I had chosen to live with my mom after they got divorced.

As I spoke with her, I learned more and more. Apparently, she and my parallel self lived here in this house with Grandma and Grandpa—but Grandpa had passed away this afternoon. The instant I processed this, I started bawling hard.

First everything with Yuno, and now Grandpa… It was all too much for my little heart to take. As I cried, Mom pulled me into a gentle hug. Back in my world, it had been years since the last time she was around to console me, so I clung to her and wailed.

Once I finally regained my composure, however, a new concern rose to mind… How was I going to get back home? That girl in the white dress wasn’t around to send me back the way I came. Was there some other way to go back? Or did I have to wait for her to hit some more buttons?

No amount of thinking would lead me to a conclusive answer. There was nothing I could do on my end except try to hide the fact that I was from an alternate universe. But while I was here…

“Mom? Could I sleep in your bed tonight?”

Surely it wouldn’t hurt, I thought to myself. After all, once I was back in my world, I’d probably never have another opportunity to cuddle with my mom… She looked surprised at first, but nodded right after that.

That night, I played with Yuno one last time, since there was no telling when I’d go back home to a world where she was gone. Then I said my goodbyes to her and climbed into bed with Mom.

***

The next morning, when I opened my eyes, I was lying down alone.

“Koyomi? You awake now, boy?”

I was greeted by a wizened old voice I knew all too well.

“Grandpa…?”

“It’s me, all right. Good morning,” he said.

“Morning…”

I didn’t understand why he was here. It felt like I was still dreaming. Did I sleep over at Mom’s place last night? I was fuzzy, but I tried to review the events from yesterday. As far as I could remember, she told me Grandpa—

I flung the blanket off and bolted upright. “Grandpa?!”

“Full of energy, are we?”

“You’re alive…?”

“What’s that supposed to mean? Don’t scare me, now!”

It was really him—but wasn’t today supposed to be the day of his wake? So if he was still alive, then…that could only mean…

I ran out of the room, out of the house, and out into the backyard. There, in an empty corner, was a small mound of dirt. Yuno’s grave.

“Yuno…”

I pressed a hand to the earth. Unsurprisingly, it was cold to the touch—no trace of the warmth I felt before I went to bed last night. Was this difference the “value of life”? It felt like the answer was on the tip of my tongue, but I was missing the final piece of the puzzle. What, if anything, was I supposed to learn from this contrast?

Frustrated by my inability to understand, I turned away from the grave. Then, to bury my shame, I started thinking about something else.

Apparently, I returned to my home world while I was asleep. I wasn’t sure why, but I was relieved to be back. That being said, what was I doing here? Last I remembered, I was in a pod at the lab. My body didn’t walk all the way here on its own, did it?

Then, it hit me. When I was sent to that world, maybe that me was sent here to my world!

So I went back into the house, found my grandpa looking at me suspiciously, and asked casually, “Hey, Grandpa? I forget—what time did I get here yesterday?”

“Hm? Good question… Ah, that’s right. Your mother went to pick you up from the lab at just past six in the evening, when my wrestling show was on.”

Mom went to the lab to get me… Now I was sure of it: the whole time I was off in that world, the other me had to have been here in my world. He must have woken up in the pod, gotten confused, and called Mom to come get him. Did he meet the girl in the white dress? What did they talk about? Come to think of it, who was she anyway?

Now I had a new objective: to find her and ask what happened.

“I will say, it’s been a long time since I last shared a bed with my favorite grandson. That was nice of you.”

“Yeah…”

Now that I thought about it, my parallel self had traveled from a world where Grandpa was dead to a world where he was still alive, so he must have been even more confused than I was. Part of me wished I could ask him about it. But hey, at least the only person I inconvenienced was myself—my other self, anyway.

“By the way, Grandpa, are you feeling sick?”

“Hm? No, not at all.”

“Good, good. Don’t die yet, okay?”

“What’s this about? I’ll have you know, I’ve got plenty of years left in me.” He ruffled my hair with a bright smile, and I could feel the warmth of his hand. But maybe that warmth would be gone in a few years’ time, like in that other world.

“I’ll come by more often,” I promised, and sincerely meant it.

“Great! I hope you find that key too.”

I never did figure out what those parting words were supposed to mean.

***

The following weekend…

“You kids have fun,” a pretty lady told us as she left the daycare.

“You should take this opportunity to make friends, Koyomi. You don’t have many as it is.” And with that unnecessary comment, my father followed suit. Now I was alone in the daycare room with the girl from before.

“So your mom’s the director?” I asked.

That lady just now was the person who founded this laboratory, and apparently she was also this girl’s mom.

After I got back to my world, I went to my dad and asked him about the girl in the white dress. He immediately identified her as the director’s daughter, and then here I was, reunited with her at the lab.

“Is that how you knew about that machine? Because of your mom?” I’d always assumed the director was some old guy, so I was shocked to find out it was a pretty lady. She and Dad apparently went to college together.

“Uh-huh.” The girl looked at me with slight trepidation. Then her eyes turned serious, and she asked, “So, did you get to see Yuno?”

“Yeah, but…I still don’t know the value of life.”

“What do you mean?”

I told her about the famous poem and explained how I was supposed to learn the value of life through Yuno’s death, but I hadn’t yet. Then I told her I kinda felt it through the presence and absence of warmth, but in my head, I was still confused.

She listened until I was finished, then smiled like I was being silly. “I think you learned it just fine!”

“Huh?”

“You’ve got it right. I’m pretty sure that difference is the value of life.”

“But how?” I asked, desperate for her to explain.

She smiled softly. “Well, her body was only warm while she was alive, right? As long as she was warm, you could play with her, pet her, talk to her—all kinds of possibilities. But when she died, she went cold. Without that warmth, her world and all its possibilities came to an end. I think that’s what you felt.”

“So warmth means possibilities…”

“Yeah! So that warmth is the value of life.”

Now I was officially convinced. Through her death, Yuno had taught me that something as tiny as a temperature change could mean a world of difference. I needed to go back to her grave and thank her. Then, and only then, I could say goodbye for real… It felt like I had finally come to terms with her passing.

“Thanks. You’re pretty cool, you know that?” I said.

“So are you.”

Her smile made my heart beat a little faster…so I decided to change the subject. “That reminds me, what happened while I was gone?”

To be fair, that was an important question. If my parallel self was switched into my body inside that pod, she must have witnessed him with her own eyes.

“Well, for me, it was like you turned into a whole different person. You didn’t know me or where you were, and you were asking for your mommy.”

“That must have been the other me! Ugh, he said mommy? What happened next?”

“Well…it was kinda scary, and I got freaked out…so…” She got a guilty look on her face, and I knew I wasn’t going to like this. “I ran away… I’m sorry.”

At first, I was a little offended that she would abandon me there. It was hardly the responsible thing to do, you know? But upon further consideration, if I were in her shoes, I probably would have done the same. So while I could get justifiably mad at her, I just…wasn’t.

“Eh, I made it back safe, so that’s all that matters. More importantly, why were you so dead set on sending me to a parallel world, anyway?”

At this, the girl fell silent for a long time. Then, finally, she said in a tiny voice, “My mom and dad…got a divorce.”

“Yours too, huh? What about it?” I replied casually.

She looked up at me in surprise, her eyes wide. Then, perhaps reassured by my lack of reaction, she continued. “They got into a huge fight—or maybe it was just Dad who was upset. He said he never wanted to see her again, and he walked out, and sure enough, he never came back. But…I didn’t want him to go…”

It seemed like her parents got divorced under very different circumstances than mine. I could kinda tell where this was going.

“Then Mom told me about parallel worlds, and how she was building a machine that could send you to one. I thought if I used it, I could find a world where she and Dad still loved each other.”

Okay, that makes sense. But how did I factor into that?

“But I was too scared to try it out myself, so…”

“So…what, you used me as a guinea pig?”

“…I’m sorry.” She slumped her shoulders apologetically.

How could such an innocent-looking girl do something so diabolical?! Was she that traumatized by her parents’ divorce? Mine were still on good terms, so I couldn’t relate. But I wasn’t about to let this slide.

“Okay then, it’s your turn to get in the pod. Right now!” I said.

“Huh?!”

“Well, we know the machine works, right? I’m living proof!”

“But…!” she protested.

I wasn’t suggesting it purely to get back at her. She may have used me like a lab rat, but I was grateful for the experience. Thanks to her, I got to have one last day with Yuno, and it taught me something important. Really, this was only halfrevenge. And to be honest, she probably needed a parallel world just as bad as I did.

As she continued to waver, I gave her one final push. “Don’t you want to see your parents in love again?”

She encouraged me that exact same way when she told me to get in the pod. Surely she’d take her own advice, right?

“Because of you, I got to see Yuno one last time,” I said. “That parallel world was exactly what I needed.”

After another long moment of contemplation, she finally nodded. “Okay, let’s go.”

“Awesome.”

Now that we were in agreement, there was no time to waste. She led me back to the room with the pod, and after asking her how to operate it (and quickly deciding she was definitely pressing buttons at random), I told her to get in.

“Just lay there and pray to go to a parallel world. That’s what I did.”

“Okay, I will.”

She closed her eyes and dutifully clasped her hands in prayer. Meanwhile, I closed the glass door and walked to the desk. I had no idea how the machine worked, obviously, so I just flipped and tapped at random, like she did for me. It didn’t appear to be doing anything, so after a while, I gave up and walked back to the pod.

“Hey, can you tell if it’s wor—”

My words petered out, and I rubbed my eyes.

Was I seeing things, or…did the girl look fuzzier than usual…?

“What in the world are you doing in here?!”

The sudden voice behind me made me jump and whirl around. “Oh… Hi, Director Satou…”

“You know you’re not supposed to be in here unsupervised! And my daughter’s with you? Come on out of there, young lady!”

The director didn’t look too angry, but I couldn’t say for sure. When she opened the pod door, her daughter sat up and hung her head in shame. She didn’t look weird anymore, and her mom didn’t comment on it, so maybe I was just seeing things after all.

“What were you two getting up to in here?” the director demanded.

“Trying to go to a parallel world,” the girl answered honestly. Incidentally, neither of us told anyone that we’d already succeeded once before. It was our little secret.

“Silly girl, the machine isn’t finished. It’s not even powered on.”

“…What?”

The girl and I exchanged a glance. The machine wasn’t finished? It didn’t even have power?!

“Wait, but—”

“You’ve inherited my innate curiosity, I suppose. And you must have gotten it from your father,” the director continued, shooting me a glance. “I admit I’m not a perfect mother, but as an adult, it’s my job to punish misbehavior. Both of you, go ahead and kneel down.”

“What?”

“Kneel down.”

“…Yes, ma’am.”

And so the two of us kneeled on the hard floor and listened to the director’s pedantic lecture for the next hour.

***

After we were finally set free, we went back to the daycare room and waited like good kids for our parents to get off work. No one else was there, and there was an awkward tension between us as we sat there in silence.

“It’s your fault we got in trouble,” I grumbled.

But she wasn’t about to sit there and take it. “You’re the one who made me go in the pod!” she protested angrily.

Unfortunately for her, I was having none of it. “Yeah, well, you started it, missy!” I hissed back, glaring at her. After all, she was the one who took me to that room to begin with.

But then, her eyes filled with tears, and I instantly regretted it. Making a girl cry was the absolute worst thing a boy could do! Did I really need to fly off the handle like that? Sure, she used me as her test subject, but I would never have reunited with Yuno without her! Was there some way I could apologize?

As I was searching for the right words, however, the girl glared back at me. “My name isn’t missy.”

At this, I suddenly realized something. The two of us had never introduced ourselves. I remembered what my dad told me earlier…

“…Sorry. I’m Hidaka Koyomi, by the way.”

Take this opportunity to make friends, my dad had said to me, and so I introduced myself. That was the first step.

When I extended my hand, the girl’s eyes widened…and then her face lit up.

“I’m Shiori! Satou Shiori.”

We shared a handshake…and that was the moment it all went wrong.

Interlude

Interlude

THAT SAME YEAR, Director Satou went to Germany to announce the discovery of parallel worlds at a major international conference.

To summarize it:

Our world is linked to dozens of alternate worlds that we unconsciously visit on a regular basis. The physical form does not travel, but rather, the consciousness is transplanted into another version of the self that exists within the parallel world. The process happens instantaneously, with no time lag.

The closer the world is to our own, the smaller the differences between the two. Often, it’s something as trivial as what we had for breakfast that morning. Furthermore, the closer the parallel world is to ours, the more likely we will travel there without realizing it, and the shorter the visit will be. This is why we don’t notice when it happens. It is this phenomenon that results in “misremembered” times and dates for social gatherings, or “misplaced” belongings that turn up in unexpected places.

It is believed that on rare occasions, humans may travel to more distant worlds that are dramatically different from our own. In those cases, the individual will feel as though they walked into an alternate reality.

Henceforth, the act of traveling between parallel worlds will be referred to as “parallel shifting.”

It was Director Satou who first named the study of parallel worlds “imaginary science.” In college, she spent years spreading awareness on the subject, and after she graduated, she established the Imaginary Science Research Institute (or ISRI) in Oita Prefecture where she was born and raised. As a result of all that painstaking research, for the first time in history, imaginary science was making headlines.

The announcement sparked unprecedented levels of debate among scholars. Scientific organizations across the globe came together to try to verify (or debunk) this lofty claim. And just three short years later, each and every international scientific authority confirmed the ISRI’s findings. Imaginary science was now an accepted field of study.

Over the years, the world around me evolved dramatically, in ways both large and small. For one thing, Shiori and I became the best of friends. Once we started spending nearly every day together, it completely changed our lives.

We went to the same elementary school, so after class let out, we’d meet up and walk to the ISRI building together. There, we’d speak to her mom, my dad, and all the other researchers to learn more about imaginary science. Suffice it to say, we knew more about it than anyone else at our school. But even then, we only understood it through simplified analogies.

Following the Yuno incident, we stopped trying to use the director’s machine without permission, so Shiori ultimately never got to take her turn. Likewise, I didn’t shift again after that—or if I did, I didn’t notice. The ISRI would eventually develop a device called an IP band that could detect those tiny, involuntary parallel shifts, but they wouldn’t conceive of it until years later.

Back then, imaginary science was still just a fairy tale to me. It wouldn’t become my irrefutable reality until the year I turned fourteen…

The year a ghost started to haunt the Showa-dori intersection.

Chapter 2: Adolescence, Part 1

Chapter 2:
Adolescence, Part 1

“I WANT TO help people.”

These words of Shiori’s kicked off our summer. As two fourteen-year-old latchkey kids with no school to attend, we spent a ton of time together, just the two of us. Hanging out, exploring—anything was better than sitting around alone at home. Our commuter bikes could take us wherever we wanted to go.

On this particular day, we met up at a park near our school to discuss our plans for the day when she suddenly hit me with those five words.

“Where did that come from?” I replied with an eye roll as we ate ramune-flavored ice cream.

Truth be told, that was a common occurrence with Shiori. I honestly didn’t realize just how weird she was until I actually got to know her. You might think she was just your average nice girl, but whenever she hyper-fixated on something she was curious about, that “nice” personality would manifest in the weirdest of ways.

For example, when we were eleven, the researchers at the ISRI caught a mouse that chewed through some papers and cables. Before they could exterminate it, however, Shiori took pity on it and demanded to adopt it as a pet. But when she tried to “train” it not to chew things, she was bitten by a tick that the mouse was carrying and became extremely ill. After that, she decided she didn’t like mice anymore.

Now, after years of enduring her unpredictable whims, I was used to her suggesting things out of nowhere, but… “Helping people” was a little vague, you know?

“You don’t like helping people, Koyomi-kun?”

“I mean, obviously I’d want to help if I saw someone in trouble, but…”

“Then let’s go help somebody who’s in trouble!” she said.

“Huh? Seriously, where is this coming from…?”

Once she set her mind on something, there was no talking her out of it. If I said I didn’t want to, she would simply leave me behind—and inevitably land herself in some kind of mess. If I wanted to look out for her, my only option was to tag along.

“Now, where could we find someone who’s in trouble?” she said, thinking.

“Well, anyplace with lots of people is bound to have at least one who’s in need.”

“A place with lots of people? Like what?”

“I dunno… Ever been to the park at the Museum of Art?” I suggested.

“No, actually, I haven’t! We should go!”

I could practically hear her mind wandering away from her initial goal, but I decided not to point that out. Her mom never took her anywhere fun, so even something as mundane as a park was enough to excite her.

On our bikes, we headed first to the train station, then traveled south for about ten minutes before stopping at a small park at the other end of the main road. This was not our final destination, however. This was the “Local Plaza,” a small section of a larger park spread out across a low hill.

As we worked our way up the incline, we reached a branching path flanked by two totem poles. This was the entrance to the other park, located inside a wooded area. From there, we followed the sculpted trail on foot up through the trees.

Finally, right as we were starting to get tired, the Children’s Park came into view halfway up the hill. Compared to the Local Plaza, this place had a better view and a lot more playground equipment, so parents liked to bring their young children here. Mine brought me here too, back before they got divorced. There was a jungle gym, a dragonfly seesaw, and an obstacle course with attached slides.

“Hey Shiori, wanna play?”

“I’m not a little kid, you know,” Shiori protested out loud, but even she couldn’t hide that telltale sparkle in her eyes.

To be fair, it was kind of pathetic to play on a playground meant for kids half our age… I bit back the temptation to relive the thrill of that giant spiral slide.

Then, after a long pause, she murmured, “Hmm… I don’t see anybody in trouble.”

At that, I took a long look around. Sure enough, everyone seemed to be having a great time. As good as it was to help those in need, it was even better not to need to.

“Let’s try higher up,” I suggested.

We returned to the park trail and set off toward the top. Shaded by trees, the summer heat couldn’t reach us, but we were sweaty nonetheless. Still, with Shiori by my side, I didn’t mind it all that much.

Breathing heavily, we arrived at the top of the trail, behind the museum. We then crossed the parking lot and climbed the stairs to our ultimate destination: the scenic vista.

“Wow… It’s so beautiful…”

The grassy hilltop was blindingly bright and filled with sunshine. At the center of the vista was a big statue that I had tried (and failed) to climb several times as a kid. On the other side of it, I could see the city streets and a tiny hint of the ocean beyond.

“What’s that building?”

“Oh, uh, the…Something House? I forget.”

We crossed the grass to the building on the other side. The sign out front read Kinderhaus. Inside, I could see moms and kids doing some kind of fun activity together.

Attached to the Kinderhaus building was a staircase that led up to the roof, and that was where I personally wanted to end our travels today. Luckily for me, no one else was around. I beckoned to Shiori, then ran up the stairs. “C’mon, the best view is up here!”

“Wow!” she exclaimed.

The view from the vista was somewhat impeded by the forest, but up here on the roof, we were taller than any of the trees. The sight of the cityscape was sincerely breathtaking.

“We can even see the mountains from here… If only we could see the ocean too…”

“You prefer the ocean to the mountains, Shiori?”

“If I had to pick one, then I guess so…”

“Huh. I’m Team Mountains all the way.”

“Don’t get me wrong, I like mountains too!” she said.

“In that case, wanna go hiking tomorrow?” I suggested.

“Yeah, sounds good!”

Just like that, the next day’s plans were set. There was a particular mountain I’d been wanting to climb for a while now, and I couldn’t wait to go there for the first time.

Seeing as we were already here, we decided to take a peek at the Museum of Art too. We didn’t know much about paintings, though, so we just kinda did a lap around the gallery and left. Since Shiori was interested in checking out the other end of the park trail, we headed downhill on the opposite side.

With no playground in that direction, there was a lot less foot traffic there. I was fine with the peace and quiet, so I took my time walking. Partway down, at the waterfront plaza, was a small gazebo. We decided to sit there and rest for a while.

“It’s nice and cool in here.”

“Yeah…”

The gazebo was positioned under the shade of the trees, and the sound of the water helped to create a refreshing ambience. So we sat there and idled away the time, waiting for our sweat to dry…that is, until Shiori exclaimed, “Oh no!”

“What’s wrong?”

“…I forgot to help people…” she mumbled.

Knew you would, I thought with a wry grin. It hadn’t escaped my notice that the fun of our adventure had gotten her sidetracked. “Shouldn’t we be happy that no one was in trouble?”

“I mean…yeah, but…” Frowning, she hung her head. Was she disappointed that she failed her mission, or that she forgot about it?

“What inspired you to start helping people, anyway?” I asked.

Sure, Shiori seemed to think up crazy ideas at random, but whenever I asked her to explain it, she always had a good reason for them.

After a long silence, she gave in. “I met up with my dad.”

At her unexpected statement, my train of thought screeched to a halt. I remembered what she told me about him—that he fought with her mom and said he never wanted to see her again before leaving for good. Did her parents make up?

“Oh, but don’t tell my mom, okay?”

Orrr not. I guess her mother wasn’t involved in that meeting.

“I thought I wanted nothing to do with him, but then I found a photo of him the other day while I was cleaning the house. I started to miss him, so…yesterday, I went to see him at his work.”

“Yeah? How’d it go?”

“He was really nice. He thanked me for coming, and ruffled my hair, and then he took me to get a big parfait. I was in such a good mood that I asked him if he and Mom could patch things up…but…he said no.”

My parents were divorced too, but mine were never on bad terms, so I didn’t know what I could say to make her feel better. Nothing I thought of seemed very helpful.

“But he did say that even though we can’t live together as a family, he’ll always love me. Even if he can’t be around, he wants me to grow up to be a good person.”

“So that’s why you want to help people?”

“Yeah. He said I should try to be the kind of person who helps others without expecting anything in return.”

“That doesn’t mean you should want people to be in trouble, though,” I reminded her.

“Yeah, I know…”

The funny thing about Shiori was that she was the type who could never see the forest for the trees. She’d focus on the end result she wanted, and when it didn’t work out, she would get so mad at herself. I thought back to the day I first met her at the lab, when she tricked me into being her parallel shift guinea pig. She was older now, but none the wiser, and those same slumped shoulders put another mirthless grin on my face.

“Well, how about you just try to help me whenever I’m in trouble?” I said, hoping to make her feel better.

I expected her to smile and nod, but contrary to my expectations, her frown remained.

“I mean, obviously I would, but…”

“What, I’m not good enough?”

“No, that’s not it. It’s just… You’re my friend, Koyomi-kun.”

“Yeah, so?”

“Well…when I help you, I won’t be able to say, ‘I’m no one special,’ you know?”

“What?” The heck is she talking about now?

“That’s what you say when you help someone without needing anything in return, isn’t it? They ask for your name, and you say, ‘Oh, I’m no one special.’ But you already know my name!”

Yep. She said that with a straight face too. Before I could stop myself, I let out a sigh. “Shiori, you can be so incredibly dumb sometimes.”

“Wha… What was that for?! I’m not dumb!” she shot back. Her eyes were teary.

I had to fight off the urge to ruffle her hair.

***

The next day, Shiori and I set out to climb that mountain like we talked about. That said, it wasn’t the hike itself that was my objective. No, my real destination was a cool spot about halfway up. The pathway was paved, so we pushed our bikes uphill with us, heaving our shoulders. On the way up, these bikes were nothing but dead weight, but once we were ready to head home, they’d make getting down the mountain a breeze! With that as our silver lining, we continued to climb and climb until we reached the parking lot at last.

I couldn’t believe how much time it took us to get here. We had left the station at three, and now it was past five. That was over two hours of travel! Granted, we might have gotten here a little faster if we hadn’t gotten lost at one point on the way. Well, that, and the slope of the mountain gradually got steeper as we approached our destination. Since the map said it was only ten kilometers, I had sorely underestimated the journey.

Anyway, the hiking part was mostly over now. We weren’t at the top yet, but the finish line was close at hand. And about five minutes later, with the help of our hand-drawn map, we found a sign that read BELL TOWER OBSERVATION DECK.

Shiori’s eyes widened. “A bell tower?”

Indeed, a monk rang this huge mountaintop bell every New Year’s Eve.

“This is the observation deck…?” She sounded a little unsatisfied as she said that.

Technically, we could see the city from here, but there were too many trees in the way to call it much of a vista. After heaving our bikes up all this way, I could understand why she might have complaints.

She hadn’t seen anything yet, however.

“Over here, Shiori.” I beckoned to her and led her to the opposite side of the bell.

“…Oh!”

A ladder descended nearly straight down from the roof of the bell tower. There was a hole just big enough for someone to pass through.

“Wait… We can go up there?!”

“Bingo,” I said.

Her eyes lit up like fireworks, and I couldn’t help but smile. This was the whole reason I brought her here—just to see those eyes.

Mt. Ryozen Bell Tower Observation Deck was located halfway up a holy mountain ten kilometers south of the train station. The bell tower itself was part of a Buddhist temple, but its roof was an observation deck. It was pretty cool. I had wanted to check it out ever since one of the researchers told me about it.

“I’ll go first. Be careful on your way up, alright?”

“Okay,” she replied.

When I got to the top of the steep ladder, I purposely avoided looking at the scenery just yet. Instead, I lent Shiori a hand and pulled her up. Then, together, we gazed out.

“Wow…”

The art museum vista we went to yesterday was only at an elevation of 100 meters max, but supposedly this place was four times as high. The view was easily a hundred times better. From here, we could even see the ocean!

“See why I wanted to bring you here?” I asked.

“Yeah… Thank you.”

Smiling, she gazed out at the scenic view. As for me, I had all the “view” I needed right beside me. Her dark, silky hair fluttered in the wind, and the breeze carried a sweet, peachy scent my way. After a few moments, I started to feel like a creep, so I hastily looked away.

Fortunately, I was rewarded with something even sweeter.

“I’m glad I came here with you, Koyomi-kun.”

She turned to me with a bashful smile, and my heart skipped a beat. Why was it racing all of a sudden? Now the blood was rushing to my face, making it burn red. Even my ears felt hot. Unable to endure her gaze, I turned my entire body in the opposite direction, praying the wind would snuff out the fire in my cheeks.

Then the conversation petered out, and for a while after that, we simply stared out at the scenery in silence. Whenever I snuck a glance at her, it seemed like her cheeks were faintly pink…or maybe I was just seeing things.

Once my own blush finally faded, and I checked the time, I realized it was almost six. Although our return trip wouldn’t take half as long, we still needed to leave soon if we wanted to get home before dark. I started to suggest we go…but then, on a whim, I stopped.

The researcher who told me about this place said the view was most beautiful at night. Being around the end of July, the sun usually set around 7 p.m. If we waited another two hours, we could see the nightscape for ourselves.

The road home would potentially be dangerous in the dark. We could get lost, and our parents would probably get mad at us for staying out past nine. But this was the perfect opportunity to see that nightscape—and Shiori’s reaction to it.

As I waffled back and forth, however, as if to direct me to the correct choice, she suddenly spoke up. “I think we should probably go home soon.”

Yes, I know that’s what we should do…but I… “The thing is, I heard this place has a really gorgeous view at night.”

“It does?”

“Yeah. What if we stay until it gets dark so we can see it?” I suggested.

At this, Shiori furrowed her brow. “But…it won’t get dark until like eight… If we stay here that long, we won’t get home until ten or so…”

“We’ll be going downhill, so it won’t take that long. We can probably get home sooner if we bike really fast.”

“We can’t go fast when it’s dark! It’s not safe!”

“But it’ll be really pretty…”

My protests faded away, and I fell silent. She was completely right, of course. However…

“Okay, you win. Let’s wait until dark,” she said.

I was so psyched, I nearly cheered out loud! But then I saw her looking at me with an exasperated smile like I was a little baby, and I started to feel really pathetic.

“You know what… On second thought, forget it. Let’s go home.” Without waiting for her, I started climbing down the ladder.

“What? Are you sure?” Perplexed, Shiori followed after me.

With no further discussion, we hopped onto our bikes and headed down the mountain path. She was right—this trail would be unbelievably dangerous come nightfall. What if she got hurt because of me? With no courage to speak, I kept my foot on the brake as we slowly worked our way down the mountain.

She rolled up beside me. “Let’s just come back sometime when we’re older and don’t have a curfew anymore,” she offered gently.

“There’s no guarantee we’ll still be friends by then,” I scoffed grumpily, despite how much I appreciated her suggestion. What in the world was I sulking about?

“Actually, I had a dream the other night,” she said suddenly.

“What kind of dream?”

“I dreamed that my future self came to see me in a time machine.” She stared straight ahead with a contented smile on her face. “She told me that you and I will be together when we’re grown up, and we’ll still be together even when we’re old and gray.”

Sounds like a nice dream.

“When you’re an old grandpa, you’ll go senile and forget who I am. Then, when I come to your rescue, I’ll get to say, ‘I’m no one special’!”

“No way. If anyone’s gonna go senile, it’s you!”

“Ha ha ha! Yeah, maybe so. But if I do, you better help me, okay?” she asked.

“Yeah, of course.”

“You mean it?”

She looked over at me with such sheer delight on her face, her eyes sparkling from all this talk of dreams…and so I answered her seriously.

“I promise, if you’re ever in trouble, I’ll do everything I can to help.”

“Okay!”

And if I had to guess…that was the day I fell in love with her.

***

Our fourteenth summers continued without incident. One fine day, Shiori and I were in the daycare room, and her mom and my dad were giving us a simple lecture on imaginary science during their work break.

“Do you know what the ‘imaginary’ part of imaginary science refers to?” the director asked. The two of us exchanged a glance. I thought I knew the answer, but it was surprisingly difficult to put into words.

“Uhhh… The ocean?”

“In an analogy, you could say the ocean, yes. Imaginary science is founded upon the concept of imaginary space, or an infinite probability space. In contrast to physical spaces that are constructed with molecules, imaginary spaces are constructed with imaginary elements. We posit that the world is composed of physical and imaginary spaces overlaid atop one another.”

Whenever she was having a serious discussion, the director switched into professor mode, and Shiori and I would raise our hands to ask questions like we were in class.

“In an analogy, those imaginary spaces are likened to the ocean, right?” we asked.

“When explaining the concept of parallel worlds, yes. But at its root, an imaginary space is any space capable of variation.”

“Variation…?”

“Change, in other words. In this world, imaginary spaces produce time, which flows on endlessly. Time is change, and paradoxically, imaginary spaces are therefore places for that change to occur. You see, change is not the result of time—change is time,” she explained.

I was fairly intelligent for a fourteen-year-old, but naturally, even I was having trouble comprehending the brilliant mind who invented an entire field of study. I glanced over at Shiori since she hadn’t spoken in a while. She was looking back at me with a confused frown on her face. I thought maybe she could help me understand, but evidently not.

Next, I sought help from my dad. Ever since the divorce, I had consistently asked him to use simple analogies to explain things, precisely in situations like these. Sure enough, he rose to the occasion.

“Let’s see…” he started. “Right, let’s say you threw a ball. Rather than the ball traveling forward over time, it’s the variation of the ball’s position that defines what time is.”

“…How does that make any sense?”

“What I’m saying is that time doesn’t actually exist. What we perceive as ‘time’ is actually countless tiny variations, one after another… Wait, maybe the best analogy is a flipbook. Each page is just a drawing, but when you flip through them in sequence, it looks like it’s moving, right? That illusion of movement is what we call time. Does that make more sense?”

“Um… Yeah, I think so,” I nodded.

From there, the director took over again. “Those tiny variations are produced by imaginary elements—the will of the universe to change. A lonely soul trying to distinguish itself from its identical siblings.”

Not only was she incredibly smart, the director was also quite poetic at times. My dad told me she was a huge fan of old-school anime, manga, and light novels, which was where she drew her naming inspirations. Unfortunately, it just made everything she said even harder for me to parse.

Luckily, there was an interpreter on standby, and my dad stepped in to help. “If we suppose that our world is a single notebook, then imaginary spaces are the blank paper. You can go through each one and draw whatever you like to make a flipbook, and all the words and pictures you add to the pages are the physical spaces. In other words, the ‘paper’ is imaginary, but the ‘ink’ you lay over it is physical. The imaginary exists to give form to the physical—without it, the physical can’t exist at all. Make sense?”

“Yeah, that makes sense.”

After all these years, my dad was a pro at coming up with helpful analogies. Without him, I’m sure I never would have grasped what the director was saying. Even Shiori seemed to understand it better now.

“Imaginary spaces are full of imaginary elements. These imaginary elements shape physical spaces, and depending on the level of variation, can create parallel worlds,” the director explained. “So, the pattern of variables in each world is what I like to call the Imaginary Elements Print, or IP for short.”

“Going back to the notebook analogy, if each different shape on a given page is its own parallel world, then the IP is the imprint of those shapes on the other side of the page,” Dad chimed in, and once again, I found myself grateful for the translation.

“Right now, my research is focused mainly on finding a way to measure a given world’s IP and quantify its variation with the worlds around it,” the director continued. “That being said, a method of observing imaginary elements doesn’t exist yet, so all we can really do is measure the physical particles to artificially estimate the IP. By reading the numerical quantification of the measured IP variation, we’ll be able to tell how distant we are from our home world. At this stage, we don’t have a prototype yet, but I’m thinking it’ll be a wearable device similar to a wristwatch.”

I tried to picture it—a watch on my wrist displaying a number indicating which world I was in. It felt like something out of a manga.

“By measuring and controlling the IP, we may even be able to move between worlds at will. This is the objective of imaginary science as a field of study.”

“Dad, are you researching this stuff too?”

“No, my research is a little different. Truthfully, I’m not supposed to talk about it.”

“It wouldn’t hurt to tell the children, would it?” the director shrugged.

Dad sighed. “I guess not… Well, imaginary science is believed to be a great step forward for scientific discovery as a whole, but if we go further, we may open the door to a whole new category of crime.”

“What kind of crime?” I asked.

“Specifically, we’re talking about IP fraud. Frame-ups, in other words. For instance, let’s say a parallel version of you stole something, then parallel shifted to this world, where you haven’t stolen anything at all. No crime, no punishment. But in exchange, you would be sent to the parallel world where you’d be punished for a theft you didn’t commit. Sounds plausible, right?”

“Wow, no kidding… So how would you fix that?”

“Well, we need to think of a way to prevent criminals from parallel shifting. That’s our job as researchers…or more specifically, my job.”

“Huh.”

Then Shiori raised her hand like a dutiful student. “Um, what if the cops just shift over and arrest him here?”

“How would they know which world he went to?” I remarked.

“Oh, good point… Hmm…”

Together, Shiori and I pondered the hypothetical. I always liked to learn new things, and with her, it was even more fun. Meanwhile, her mom and my dad started muttering to each other and shooting us furtive glances for some reason.

Suddenly, during a pause in our discussion, the director asked us a question. “Are you two together?”

It was so out of left field that we both froze.

“I suspected as much myself,” Dad commented.

As for what they were referring to, it was Shiori who processed it first.

“Wh… What are you talking about?!” she shrieked angrily. “Koyomi-kun and I aren’t like that! Don’t make it weird, Mom!”

Though she was often just as eccentric as her mother, Shiori was generally a more reserved person. That was the first time I ever saw her lash out at her mom.

As for me, I should have understood what was implied by “together” and “like that,” but for whatever reason, my brain took an extra-long time to comprehend it…and when I finally grasped that they thought we were romantically involved, I couldn’t help but felt hatred toward so-called “adults” for the first time in my life.

Admittedly, yes, I had become conscious of my feelings for Shiori just the other day. But I wanted to take it slow, at my own pace. Sure, maybe she would agree to go out with me if I asked her right this second, but I wanted to spend time cultivating a natural transition from friend to something more. After all, that was how we kindled our friendship to begin with.

Why were they even asking us this? What were we supposed to say? It felt like Shiori and I were in the middle of painting a picture, but these stupid adults had walked up and smeared a new color onto our canvas without asking. Now we could never achieve the result we originally wanted.

That was the first and only time I hit my dad. “Screw you!” I yelled.

Looking back, this was the start of a late-blooming rebellious phase that Shiori and I, unlike a lot of other fourteen-year-olds, had thus far never had. Dad and the director both stared at me, mouths agape, like they had no idea why I’d lashed out. But when Shiori saw me strike at my father, her anger toward her mother was overwritten by concern. This only made me feel worse. Frustrated, I turned away from the adults.

“Shiori, let’s just get out of here.”

“…Okay.”

As I left the room, she dutifully followed me. For a second, I was tempted to grab her hand…but decided against it.

After that, we found a riverbank and took turns skipping rocks and talking smack about our parents. That said, neither of us had much experience with this “teenage rebellion” thing, so our insults were a little weak.

“Rrgh, I can’t believe her! Why would she say that to us?” she said.

“It doesn’t make any sense. Like, what does it matter if we were?”

“And your dad said he ‘suspected as much’…”

“Suspected, my ass. He thinks he knows what love looks like? He couldn’t even stay married to my mom!” I yelled.

“Same as my mom. She made my dad so upset…”

“They had no right to say that to us… I should have punched him harder.”

Fueled by anger, I flung another rock at the river. My frustration was out of control. “Koyomi-kun and I aren’t like that,” Shiori had said to her mother. Those were words I never wanted to hear, yet here we were.

Looking back, it all made sense. I never acted on my feelings for Shiori because I wanted to leave our relationship just ambiguous enough to avoid having to hear that. But now, she’d been forced to say them.

“I mean, we’re not even like that, you know?”

“…Yeah.”

Thanks to our parents, our friendship now had hard limits.

***

Perhaps it’d be too much of an exaggeration to say that was the day my world began to collapse. However, I can say with full sincerity that it was from then on that my life quickly started to lose its color.

On August 15th, my dad and I went to Mom’s house to celebrate the Bon Festival for the first time since Grandpa passed away the year prior.

After I hit Dad, I spent every subsequent day out and about with Shiori for as long as possible, so I wouldn’t have to be around him. Whenever I had to be home, I stayed cooped up in my room. This worked for a while, but unfortunately, family holidays refused to be ignored.

My mom was born an only child, so the only relatives at the house were my great-aunts, great-uncles, and my second cousins, none of whom I recognized. I knelt on the floor until my legs went numb, listening to the drone of the monk’s incomprehensible Buddhist chanting. After that, I smiled evasively while middle-aged women I barely knew told me I was “all grown up now.” Anytime an intoxicated great-uncle came over to ramble at me, I ran away to the bathroom.

Finally, at the end of the night, after all the distant relatives had left, it was just me, Mom, Dad, and Grandma. Together, the four of us cleaned the house. Grandma then went to bed early, and for the first time in ages, it was just me and my parents.

As we sipped the tea Mom made for us, I shifted uncomfortably. Meanwhile, she struck up a conversation like it was any other day.

“Thanks for coming. I know it couldn’t have been pleasant.”

“Well, you’re an only child.”

At first blush, it may have seemed like their exchange didn’t make sense. But the way I interpreted it, Mom was saying he must have hated attending his ex-wife’s family reunion, and Dad was saying it was no big deal since it was nothing but distant relatives. It was this “minimalist” conversation style, so to speak, that had caused their divorce in the first place, but Mom actually seemed to be enjoying it for a change.

“You’re staying the night, right?”

“Nah, I’m heading home. Koyomi can stay if he wants though.”

“Yeah, I will,” I answered brusquely. It was my plan all along, since I still wanted to avoid him as much as possible.

However, Mom must have sensed something in my tone. “You’re not fighting with Daddy, are you, Koyomi?” she asked with concern.

“No.”

“He’s just going through a phase. He’s at that age now,” my dad said.

“Right… Eighth grade, huh? Have you settled on a high school?”

“Either Uenogaoka or Maizuru.”

“Ooh, the big leagues! I’m sure you’ll make it. You’ve got your father’s smarts.”

For some reason, being compared to my dad was enraging me like never before. Hadn’t I wanted to be a researcher just like him until recently?

“By the way…” Dad trailed off and straightened up in his chair. “I wanted to have a family discussion about something.”

“What is it?” Mom asked. I was similarly clueless. What could he possibly need to discuss with both of us?

Then, a possibility occurred to me. The chances were microscopic, but…what if he wanted to get back together? His relationship with Mom was never truly damaged beyond repair, and they had stayed on good terms long after the divorce. These past few years of living in a two-guy household we hadn’t exactly needed Mom, but there were plenty of times when I wished she was around. Surely Dad felt the same way…right?

The root of their divorce was poor communication. My scientist father had always spoken to Mom like she was a colleague. But now that I’d spent the past few years training him to use simple analogies, that issue was essentially solved. At the very least, he knew to use bubbles to explain difficult concepts like imaginary science.

Plus, with Grandpa having passed away, Mom and Grandma were all alone in this huge house. She never talked about marrying someone else either…

Maybe Dad saw this as a chance to try again…?

Dad looked from me to Mom. He said, “I’ve been thinking about getting remarried.”

My first reaction was YES!

But when I heard Mom’s response, I realized I had misunderstood.

“Who’s the lucky lady?”

Wait, so…it’s not you? Then…who is it? I’m going to have some other mom? It felt like my whole world had been turned upside-down. I was so confused, I failed to process my dad’s next words.

“Director Satou at the laboratory. I believe you know her.”

Director…?

“A-ha. Yes, I think I saw that coming,” my mom said.

“She’s been divorced for a few years herself, and right now she lives with her daughter, who’s the same age as Koyomi.”

Daughter, same age as me…?

“Then it sounds like he’ll have a new sister. Older or younger?”

“Younger. As I recall, his birthday is ahead of hers,” he said.

Wait, slow down. I don’t get it.

“Has he met her before?”

“Met her? They’re such good friends, they go on adventures together every day.”

But there’s only one girl I hang out with every day…

“I see. Sounds like they’ll be very close siblings,” Mom remarked.

Me and…Shiori? Shiori’s going to be my little sister?

Admittedly, I had yearned to be more than friends with her, and “family” was one way to achieve that, but…no! That was not what I wanted!

As my brain stalled out, however, my parents carried on without me.

“Have you already broached the subject with her?”

“Yes, she said she’d speak to her daughter about it tonight.”

“Is this the first Koyomi’s hearing about it?”

“Yeah.”

“Well then, you ought to ask him.”

“Right. Koyomi, you know the lab director? Shiori-chan’s mother?”

“Yeah,” I answered my father reflexively, my mind still blank.

“Would you be opposed if she became your new mom?”

“No…” Honestly, I didn’t object to having the director as my new mom. But Shiori being my sister?

“I see. Thank you. It won’t happen right away, but I’d like it if you’d come back to the lab and take some time to get to know her better.”

“Okay,” I answered without thinking, then immediately regretted it.

“Well, I suppose I ought to congratulate you,” Mom remarked.

“Thanks. I hope you find someone special too.”

“Ha! Do you realize how old I am now? Women can’t start over the way men can.”

“They can’t…?”

“Trust me, we can’t,” she said.

“Come now, surely you can. You’re a very charming woman.”

“Not charming enough to keep our marriage together.”

“But I was the one who—”

“Stop! You have a habit of trying to take the blame without listening to how the other person feels. Sometimes things just aren’t your fault, and you need to accept that!”

“…Who are you and what have you done with my ex?”

“Hee hee! I’ve always wanted to say that to you, ever since we ended things.”

“You really are quite charming, you know that?” my dad said to her.

“Thank you. Perhaps with your encouragement, I’ll wade a little deeper into the dating pool myself.”

Mom and Dad continued to have some sort of conversation that I wasn’t old enough to comprehend. Meanwhile, I could only think of Shiori. As my new sister, we’d spend even more time together—that part I liked. But that wasn’t what I wanted. I didn’t want a sister.

Still, I couldn’t help but wonder… What did she want?

According to Dad, she and her mom were having a similar conversation right about now. Was she thinking the same thing I was, or…?

***

The day after I slept over at Mom’s house, I didn’t feel like going home, so I invited Shiori to hang out. We met at a park near our junior high, and then we started discussing what to do like it was any other day. If her mom had talked to her about marrying my dad, she was hiding it flawlessly behind her usual smile.

“Listen, Koyomi-kun, there’s somewhere I want to go today.”

That was uncommon. Usually, I was the one who suggested where to go based on recommendations from friends or researchers at the lab.

“Where’s that?”

“Tanoura Beach,” she said. “Ever been?”

“Oh yeah, by the aquarium? I think I went there once a long time ago.”

It was about thirty minutes away by bike, but since we’d be traveling along the highway, the road would be wide and paved—perfect for a little recreational cycling. Plus, the beach was the ultimate classic summertime destination.

“That’s where I want to go.”

“Cool, but we’ll need to go home and get our swimsuits.”

“No, we don’t need to swim. I just want to go there and talk.”

It felt like a missed opportunity to me, since we’d be right there at the beach…but on second thought, maybe it’d be awkward to go swimming with a girl in a one-on-one setting. And so the two of us hopped onto our bikes and set off.

With the ocean in view, we traveled north along National Route 10 for thirty minutes until we could see a seaside park coming up on our right-hand side. Tanoura Beach. There was no entry fee, so it was a great place for kids to hang out unsupervised. We parked our bikes in the parking lot and started walking along the promenade.

Summer vacation was still going strong, yet somehow the place wasn’t as packed as I expected. Maybe it was because all the major summer holidays were over by now. Still, there were tons of people swimming in the ocean, and given how sweaty I was, I was dying to dive in with them. Fighting the urge as I walked, I soon caught sight of a boat-shaped playground fixture out on the sand, with little kids swarming it like ants.

“Ever gone in there, Koyomi-kun?”

“Just once.”

“What’s it like inside?”

“Uhhh… I was pretty little, so I don’t remember.”

“Darn. I wish I could go in there.”

“Just go for it!”

“I can’t barge in on all those little kids!” she said. But the look in her eyes told me she’d kill to do just that. The only problem was, it’d be awkward to join in with kids half our age…

Wait, why am I getting déjà vu?

What made Tanoura Beach special was the pier leading out across the water to a tiny man-made island called Tanoura Isle. If you followed the little path around the isle, you’d see palm trees and people reclining on the grass in their swimsuits like you’d been transported to a tropical resort. Looking out across the ocean would give you a glimpse of industrial buildings in one direction and the famous monkey park in the other… Point being, this place had a lot to offer.

Shiori slowed to a stop and turned toward the ocean. “Gorgeous, huh?”

She gazed out straight north, where the entire view was nothing but blue sky and blue ocean—so blue, it felt like it was going to suck me in. If the guardrail wasn’t there, I swear I might have unconsciously taken a step forward and plunged straight into the sea.

“Wanna have a seat somewhere?” I asked her. There were benches on this side of the isle, and I could see an empty one right under the shade of a palm tree. But when I suggested it…

“No, let’s talk over there.”

She pointed to a roofed rest area hanging over the grass. A small bell hung over the wide entrance, like a chapel…and incidentally, it was the exact spot I had been hoping to avoid.

The last time I came here, I was with my parents. My mom pretended to hold a wedding right in that very spot. That was before they decided to get divorced. Now, with the topic of remarriage hanging over me, I would have preferred to steer clear of anywhere that brought weddings to mind.

But Shiori wanted to come here today, and as far as I knew, she had the same conversation with her mom that I had with my dad. She clearly wanted to talk about it.

“Okay, sure,” I conceded, and the two of us stepped into the fake chapel.

Honestly, the only thing “chapel-like” about this place was the entrance on the south side. The other sides didn’t even have walls. But when you sat down on one of the wooden pews, you could almost trick yourself into thinking you walked into a church.

Shiori sat beside me, and for a while, she didn’t speak or move a muscle. But just as I started to worry that maybe I needed to initiate the conversation, she finally broke the silence.

“Did you hear?”

“…Yeah.” No need to ask what she meant.

“Crazy, huh?”

“Totally. Like, yeah, I saw ’em together at the lab a lot, but I figured it was for work.”

“Your dad is the vice-director, after all,” she remarked.

“What? He is?”

“You didn’t know?”

“No! I mean, I knew he was somebody important, but…” I trailed off.

“Well, did you know they went to college together?”

“Yeah, he told me they set up the lab together.”

“You think maybe they were dating at the time?”

“No, Dad was already dating my mom in college.”

“What, really?” Shiori asked.

“Yeah. Last night, Mom was telling me the story of how they met when they were both at school. Supposedly, she was the one who asked him out.”

“So the three of them all went to college together?”

“No, no, Mom went to a different school.” I said. “Apparently, she met your mom through my dad. She said whenever they hung out as a trio, the other two would always get into these super complex conversations and leave her hanging.”

“…How does she feel about him getting remarried?”

“She said she saw it coming.”

“Oh.” Shiori fell silent at that.

I didn’t know what went on between Mom, Dad, and the director, or the details of how they all felt about each other. I never asked, and I wasn’t planning to—it was none of my business. I only took issue with the part that affected me and Shiori.

“Koyomi-kun… How do you feel about my mom being your mom?”

“That part I don’t mind at all. Sure, she’s a little kooky, but she’s cool, and she’s always teaching me stuff. Oh, and she’s really pretty.”

“Um… Thank you, I guess?”

“What about you? Think you can accept my dad as your dad?” I asked.

“Yeah, I don’t mind either. Same as what you said—he’s weird but cool, and I’ve learned a lot from him.”

“Sounds like our parents have a lot in common.”

“Yeah. That must be why they’re compatible.”

The conversation petered out again. This wasn’t exactly what I wanted to talk about. I wanted to ask her how she felt about us being siblings, and I was pretty sure she wanted to know the same thing. However, I suspected neither of us were prepared to answer that question ourselves…and we were both afraid to find out what the other would say. Much as it shames me to admit, it was Shiori who found her courage first. Maybe a “real man” would have broached the topic first, but I just couldn’t do it.

“I, um… I kinda thought…”

I glanced at her face in profile. She was nearly expressionless, her eyes squinting out at the sea. But…behind the long strands of dark hair, her cheeks…

“I thought you and I would get married someday.”

As she said those words, her pale cheeks lit up scarlet. Instantly, my mind went blank. She slid her hands between her knees and hunched over, and I suspected the sweat on her face was from more than just the heat.

“But…siblings can’t get married, huh…” she squeaked out.

All the fears and feelings I had—she had them too? It wasn’t all in my head? She didn’t think of me as just a friend? She wasn’t fine with being my sister?

In that instant, every last worry went straight out the window.

“Shiori!” I grabbed her by the shoulders and turned her to face me.

“Huh…? Wha…?”

She gazed back at me with damp eyes, her cheeks still flushed pink. And so, without stopping to think, I hit her with the first words that rose to my mind.

“Let’s run away together!”

***

It was the “summer elopement” that would never be.

The next day, Shiori and I used our newfound momentum to pack our bare necessities, leave our houses, and hop onto our bikes with the intention of never going back.

“Where should we go?”

“Mmm… Anywhere’s fine, as long as I’m with you, Koyomi-kun.”

An exchange so cliché, we may as well have been reciting lines from a movie, but I loved it all the same.

At midday, our spirits were high. We walked around town having a blast. The moment I enjoyed most was when we went to the home furnishings section of a big department store and talked about what we’d buy if we got a house together. At the time, I was genuinely thinking only of our future, just the two of us—most likely to escape the reality of how I knew, deep down, this elopement was destined to end.

Once the sun started to set, we began to brainstorm where to spend the night. To prioritize safety, we chose a park close to the corner store and the police station. Then we laid a tarp under a spot with a roof to make a simplified bed. However…

“Good evening, you two. Got a minute?” A policeman on patrol walked up to us. “Do you live around here? Is your mom or dad with you?”

“No, uh… We came here for fun…”

“I see. Well, it’s getting dark out, so you’d better head home now.”

“Okay, we will. Let’s go, Shiori.”

“Uh, okay.”

So we folded up our tarp, grabbed our stuff, got back on our bikes, and left the park.

As it turned out, when junior high schoolers stayed at a park past dark, the cops took notice. Every time a patrolman flagged us down, we told him we were going home, then got on our bikes and headed farther out of town. Ultimately, we settled for the night inside an abandoned air-raid tunnel four kilometers from the nearest train station. Here we could be sure that no one would find us, and with walls and a ceiling, we were mostly safe from the elements. It was scary for a different reason—but as long as we were together, I was sure we’d be okay.

What wasn’t okay was…well, everything else.

In the pitch-black tunnel, we lay side by side on the tarp, each of us huddled up under thin summer blankets we brought from home. It was nice and cool in there, much more pleasant than outside. Technically, we did have a light source—a battery-operated lantern—but we couldn’t use it without attracting moths, so instead we stayed in total darkness, holding hands and discussing our next move.

“…This is impossible, huh?”

“Yeah…”

By that point, both of us had come to our senses.

“I brought all my money, but if we sleep at internet cafes every night, it’ll be gone quick. But we can’t sleep outside forever…and we gotta buy food… Honestly, I’m not sure I can even make it through tonight.”

“Yeah… Plus, I want to take baths and have clean clothes…”

It wasn’t like Shiori and I hadn’t known it would be this hard from the outset—we simply chose to pretend we hadn’t. We were both deep in denial.

“When we wake up tomorrow, wanna take a train somewhere far away? We could look for live-in jobs or something,” I suggested.

“That could work. Or what if we look for an abandoned railway? Maybe we could find an unused train car and turn it into a house.”

“Ooh, that sounds fun! Like something in a manga!” Alas, my hopeful smile quickly clouded over. “…Man, there’s no way a couple of junior high students could remodel a train car or get live-in jobs in real life.”

“If only we were in high school, at least…”

“We could wait two more years and try again.”

“But we’ll be siblings by that point…”

Once we were siblings, we really could never get married. Right now was our only chance to run away. But realistically speaking, junior high schoolers couldn’t make it on their own.

“If only Mom never got divorced,” Shiori muttered. “That way we’d never have to be brother and sister, because she’d never want to marry your dad.”

“Same here. I wish my dad never got divorced either.”

All we could do now was cry over spilled milk. We had no optimism left. Was our only option to go home like good little children, congratulate our parents, and live the rest of our lives as brother and sister?

“If only my mom—”

Just then, Shiori stopped short. There in the silence, I couldn’t even hear her breathing. Was she holding her breath? What had gotten into her all of a sudden?

Could the cops have tracked us all the way here? Was there a stray dog or something? Whatever it was, I could tell it was serious. Gripping her hand tightly, I shifted my position so I could jump up at a moment’s notice.

“What’s wrong, Shiori?”

“…I’ve got it.” Her hand squeezed mine back.

“Got what?”

“A way out for us.”

Her statement was abruptly and completely out of left field. A way out? Where could we possibly go to escape being siblings so we could get married?

“What is it?” I asked.

Now that my eyes had adapted to the darkness, I could see the outline of her figure. She leaned in quickly, her body heat suddenly inches from mine. Now I was grateful for the dark concealing my panic.

“A parallel world,” she whispered breathily.

“…What?”

“A parallel world, Koyomi-kun! Remember when you went to a world where Yuno was still alive? There’s gotta be a world where our parents never got divorced. If we go there, we won’t have to be siblings!”

Her words seeped into my brain, and it truly felt like a veil had been lifted.

“That’s it… That’s it, Shiori! How did we not think of it sooner?!”

“I know, right?! You already did it once, so I just know we can do it again!”

If we both went to a world where our parents were all still together, the two of us could get married like normal. It was the perfect solution!

“Well then, guess we gotta go to the lab. I wonder what happened to that machine.”

“Last I heard, it’s still unfinished, but… I mean, you already used it to parallel shift, like…four years ago now, wasn’t it?”

Four years felt like an eternity. That incident was what brought Shiori into my life.

“Right. At the time, your mom said it was both unfinished and not even powered on. But I swear I shifted to a world where Yuno was alive.”

“Maybe the machine is finished, but Mom just doesn’t realize it yet.”

“Either that, or maybe only kids can use it? You see that kind of thing in manga and stuff,” I remarked, conveniently forgetting that just moments earlier, I’d acknowledged that real life never worked out like it did in manga.

“Wait, so… Do we still count as kids, or…?”

“I don’t know, I was just spitballing. Maybe I’m wrong, but…I mean, we’re not adults, so we gotta count as kids.”

“Right… If we were adults, we wouldn’t be having these problems.”

Indeed, if we were all grown up, we wouldn’t be camping out in an abandoned tunnel. We’d be free to live on our own, away from our parents.

“Well, if we’re gonna do this, we better act fast,” I said offhandedly.

Shiori looked up like it was precisely what she’d been waiting for. “Wanna go now?”

“Now?”

“Yeah! You know the lab tends to stay open pretty late! And it’s only eight, so I bet they’re open! It’ll be easier to sneak in with hardly anybody around!” she blurted out, all at once. It reminded me of the day we met—the day she dragged me off on our first adventure.

“Right… Yeah, you’re right! Let’s go!”

Together, we packed up all our things, jumped on our bikes, and set off to the laboratory. Once again, though there was no evidence that we would succeed, we charged forward purely on the thrill of our seemingly revolutionary plan. Small details be damned. This prospective parallel world, propped up on our biased theories, was our sole hope.

A world where Shiori and I could be happy together…

***

Sure enough, the lights were still on at the lab, just as Shiori suspected. She opened the rear exit with a practiced hand, then walked straight through the cluttered maze of a building while I scrambled after her. After all these years, she still knew the layout way better than I did.

The interior was mostly deserted because at this hour, the majority of employees were already gone. That worked in our favor, so we sped down the hall like ninjas until we arrived at a familiar door. Shiori grasped the knob and slowly turned it—but there was a small rattling sound, and it refused to twist all the way.

“It’s locked, huh?”

Of course it was. Granted, it wasn’t originally locked four years ago, but they must have decided to start locking it after that incident. This posed a problem. How were we supposed to get in?

“No worries.” Shiori pulled a key out of her wallet.

“Is that…?”

“A spare key. I had it made in secret, just in case,” she explained casually, like she’d done nothing wrong, as she unlocked the door. She was normally a well-behaved girl, but when it came to sating her own curiosity, she was willing to bend any rule that stood in her way. Well, in this case, it paid off.

We entered the room and shut the door behind us. To avoid being detected, we left the lights off and used the flashlight function on our phones to illuminate the floor as we approached our destination: the pod.

“Long time no see.” I hadn’t been in here since the day I parallel shifted four years prior. Frankly, I never dreamed I’d climb back into this thing. “Looks like it’s still not powered on. Think it matters?”

“It didn’t matter four years ago, right? Let’s just get in.”

“Okay.” I opened the glass door. The cramped space within looked to be designed for a single occupant. “Who’s going first?”

“What? We have to go together! The whole point is that we have to go to the same world, remember?”

I was indeed aware of that, but had chosen to play dumb. Were we really going to wedge ourselves in there? Both of us? “I mean, if it’s meant for one person…”

“Well, we can just… Um… See, we’ll both fit if we go in like this.”

She climbed in ahead of me and rolled onto her side, nestling into the left half of the pod. A-ha. Now, if I could position myself into the right half, we’d both fit. She’s dead set on this, huh? Well, okay…

“All right, I’m getting in.”

With a fair amount of ulterior motive on the back burner, I twisted myself into the right side of the pod, trying my best not to brush against her. But in a space that cramped, it was inevitably a tight fit, and we were packed in like sardines, face-to-face.

“…Huh?” Just then, bathed in the light from my cell phone, I realized Shiori was blushing. “Wh-what’s the matter? You’re the one who told me to get in here with you!” I stammered, quick to shove the blame on her. My face was probably turning red too. And with her next words, it would only get redder.

“Yeah, but I…I thought you’d face the other way…”

Oh. Yeah, that was probably what a normal person would do. “Um… S-sorry! I’ll get out!”

“Wait!” Before I could clamber out, she grabbed my arm. “It’s fine. Let’s just do it.”

“But—”

“It’s fine!”

“…Okay.”

At her insistence, I settled back into the pod and faced her at point-blank range. I could feel her body heat, smell her scent, even feel her breath against my skin… It was a miracle that she couldn’t hear my heart jackhammering nonstop against my ribcage.

“Wh…what now?” My voice cracked as I spoke. Ugh, pathetic.

“Well, um… What did you do when you shifted four years ago?”

“You told me to pray, so I did. I prayed to go to a world where Yuno was alive.”

At first, I only did it as a joke, but partway through it turned completely serious. Of course, I couldn’t say for sure if it actually helped me shift.

“Okay then, let’s do that. Let’s both pray to go to a world where our parents aren’t divorced.”

“Think that’ll be enough, though? Last time you stayed outside the pod and messed around with the machine. Maybe you happened to flip the right switch.”

“But my mom literally said the machine wasn’t powered on. Pretty sure it doesn’t matter.”

“Oh, right… Yeah, maybe it doesn’t.” Trusting in our biased conjecture, we chased our single ray of hope. “All right, I’m gonna close the door.”

“Okay.”

With the door shut, her presence seemed to magnify beside me. Then we closed our eyes and began to pray.

Take us to a parallel world. A world where neither of our parents got divorced. A world where we’ll never be brother and sister. A world where we can be together!

Out of nowhere, Shiori wrapped her arms around my waist and snuggled in closer. It startled me, but I quickly did the same in kind, embracing her petite frame.

“Koyomi-kun…” She sounded scared.

“Don’t worry. We’ll make it there,” I reassured her as firmly as I could manage.

“I know. When you get to the other side, come find me, okay? Find me and make me your wife.”

“I will, I promise. We’ll get married.”

Our arms tightened around each other—

***

Fluorescent lights dazzled my eyes. Just moments prior, I was in a pod in a dark room, but now I was somewhere much brighter. I closed my eyes, then slowly opened them to find out where I was.

This was, beyond a shadow of a doubt, my bedroom—but upon further inspection, I spotted some manga on my shelves that I had no recollection of buying. This had to be a parallel world! Step one was a success. Now I had to find out if my parents were divorced.

I recognized this room from the same house where the three of us used to live together. After they got divorced, however, Mom moved out. So if I found her somewhere in this house right now, it would more or less confirm that they were still together.

I checked the clock—it was just past 9 p.m. If Mom was here, she’d still be awake. After two or three deep breaths, I slooowly opened my bedroom door. I could faintly hear the sound of the TV coming from the living room. Was my dad home, or…?

For some reason, I found myself creeping on tiptoe to the living room door. Then I put my hand on the knob, twisted it, and silently inched it open. There on the couch, channel-surfing, was none other than…

“Mom!”

“Jesus, you scared me! Silent as a ghost—gave me a damn heart attack!”

When she whirled around to look at me, my suspicions were confirmed. It was my mother, and if this was my world, she wouldn’t be sitting here right now.

“Sorry, Mom… What are you doing here?”

“Huh? Can’t a woman watch some TV?”

“No, I mean… Yeah, of course. But, um…where’s Dad?”

“Still at the lab. I’m sure he’ll be home late, as usual.” She shrugged like this was a normal conversation—probably because living here was normal to her.

I was convinced. This had to be it. “Hey Mom…can I ask a dumb question?”

“What sort of dumb question?”

“Um… You and Dad are still together, right?”

God, I’m so stupid. Surely there had to be a better way of asking! Her jaw dropped as she blinked back at me in confusion. No surprise there. In a world where they weren’t divorced, this question would sound extremely weird.

But then, for some reason, her confusion turned to sympathy.

“I’m so sorry you had to see that, sweetheart, but everything’s okay now. Mommy and Daddy aren’t getting divorced,” she said.

Yes! YES! In this world, my parents were still together! Based on what she said, it sounded like there was a point at which divorce was on the table, but in this world, they made things work! That meant my dad was still married—and that meant me and Shiori—

“Oh, right! Shiori!”

I just remembered. Did she make it to this world too? I checked my phone but couldn’t find a contact entry for her. Had I not met her in this world? If so, then as of today, that was going to change. If Shiori and I were both here, we were going to… Well, maybe we wouldn’t get married right away, but you know.

So what now? I wanted to see her as soon as possible, but where was I supposed to find her? I cursed myself for not having the forethought to set a meetup spot beforehand. I assumed we would end up in the same spot together, but I forgot that parallel shifting meant trading places with our parallel selves.

In that case, perhaps my best bet was to go back to the lab where we just were. Maybe Shiori would have the same idea. Even if she didn’t, I could just ask my dad to ask the director to get in touch with her.

And so I decided I would go to the lab. I could just say I was going to wait for Dad to get off work, right?

“Koyomi, what’s the matter?”

As I stood there, embroiled in my thoughts, Mom looked at me with mild concern. Right—my behavior probably seemed strange to her. Sorry, Mom, but I don’t have time to worry about that right now!

“I’m gonna go pick up Dad from work, okay?”

“What? Now wait one minute, Koyomi! Seriously, what’s gotten into you?”

Ignoring my mother’s confusion, I headed for the front door. Really sorry about this, but I gotta find Shiori ASAP! I’ll explain later, I promise!

I grabbed a pair of shoes I assumed were mine from the shoe box and put them on. They were the perfect size, and they matched the shape of my soles from frequent use, so they had to belong to my parallel self. Well, starting today, they were mine. This whole world was mine! Here, I’d carve a path to a future with Shiori—

***

And then there was only darkness.

“Huh?”

Thrown suddenly into shadow, it felt as though the blackness was adhered directly to my eyeballs. Of course, that wasn’t actually the case. Over time, my eyes adapted enough that I could see my immediate surroundings.

I was lying on my side in the cramped pod, my arms wrapped around something soft and warm. Then I smelled that familiar shampoo…and realized it was Shiori. Suddenly, out of nowhere, I was holding her in the dark. Had I been sent back to my home world? Why? It was going so well!

Had Shiori shifted back too? Had she even made it there to begin with?

“Hey, Shiori? Can you tell me what just happened?” I whispered.

She didn’t answer.

“Shiori? What’s wrong?”

I tried again. Still no answer, but I could definitely feel her weight and heat right there in my arms. Was she asleep? Or was she off in that parallel world still? In that case, wouldn’t her parallel self be here in her place?

“Hello? Shiori, wake up! Shiori?”

I pinched her cheek. No reaction. Then I realized something critical. Here in the cramped pod, there were a lot of ways for me to feel her presence. Her body heat, her sweet scent, and…her breath.

“…Shiori…?”

Our lips were practically touching, and yet…I couldn’t feel her breath against my skin.

“Shiori? Shiori?!”

I put a hand up to her mouth and tried to feel for it with my palm, but no dice. She isn’t breathing? Why isn’t she breathing?!

“Shiori! Shit, we gotta get you out of here!”

I tried to open the glass door, but it refused to budge. Then I realized our most critical mistake: the door on this pod didn’t open from the inside! What else could I do? Scream for help? But then they’d find out that we snuck in… Screw it!

“HELP! IS ANYBODY HERE?! WE NEED HELP! PLEASE!!!” I hollered at the top of my lungs while banging on the glass door. At least one researcher was bound to still be working at the lab. They had to hear me!

And sure enough, as I was making the biggest commotion I could manage, the lights suddenly clicked on. Someone had come to the rescue!

“WE’RE IN HERE! LET US OUT!!!” I screamed louder than ever before.

“Koyomi?! The hell are you doing, son?!”

On the other side of the glass, I saw that my savior was—for better or for worse—my own father.

“Oh, and my daughter’s with him. I really thought you two learned your lesson…”

I saw the director standing beside him too. Ideally, I would have liked to keep those two in particular from ever finding out about this, but that didn’t matter right now. They opened the pod door, and I came scrambling out.

“Didn’t we tell you not to come in here without permission? I’ll have you know that this machine—”

“It’s Shiori! She’s not breathing!” I yelled, interrupting the director.

At this, she and Dad exchanged a glance—then pulled Shiori out of the pod without another word. Normally they’d demand answers to a thousand questions, but they both quickly realized Shiori’s condition was far more pressing. After a few seconds of observing her current state, the director started calling someone on her phone.

“It’s me. Got an emergency patient with special circumstances. We need an ambulance ASAP.” With that, she hung up and immediately started blowing into Shiori’s mouth while Dad gave her chest compressions.

As for me… I couldn’t comprehend what was happening right in front of me. I just stood there, staring blankly, as the two of them fought like hell to keep Shiori alive.

***

When the ambulance took Shiori to the nearest hospital, she was accompanied not only by the director, but by me and my dad as well. While the doctor was examining her, naturally, the two adults demanded an explanation from me.

“What in the world is going on, Koyomi? Use your words and tell us,” Dad said calmly, with no hint of anger. The director seemed normal too—on the outside, at least.

“…We were trying to run away to a parallel world.”

“Run away? Why?”

“Because you two are getting married,” I admitted honestly.

They looked at each other, their eyes wide in shock.

“So you were opposed to it? I thought you said you were fine with the director as your new mom!” my dad yelled.

“I am fine with that. It’s not about her… I just don’t want Shiori as my sister.”

“Why not? I thought you two liked each other a lot.”

“Yeah, and that’s why.”

Neither my dad nor the director seemed to grasp what I was getting at, so I was forced to spell it out for them.

“Once we’re siblings, we can’t get married. Duh.”

At that, Dad finally understood. “So you do have feelings for each other. When we asked you, you both denied it, so we thought…”

He must have meant that time I hit him. If I could have admitted it outright then and there, would things be different now?

“We were blind, Hidaka-kun. When they told us it wasn’t like that, we took them at their word, never realizing the truth… Yes, we were blind indeed,” the director repeated, shaking her head weakly. For some reason, I started to feel guilty.

“Well, Koyomi, to be clear, you’re wrong about one thing: Step-siblings can in fact get married.”

“…What?”

“It’s perfectly legal as long as you’re not related by blood, which the two of you obviously aren’t. No parallel worlds necessary.”

Excuse me?No one told me that! I’d thought all types of siblings were forbidden to marry. If I’d known that wasn’t the case, this never would have happened.

“So you’re saying…everything we did…”

“…It’s not your fault. You didn’t know any better. And it’s partly our fault for being insensitive to your feelings… Now tell us, Koyomi. What exactly did you two do in there?”

I was prepared to confess everything. It was now painfully clear that our childish plan was destined for failure from the very beginning. Thus, the best course of action was to be honest about every last detail so the adults could fix this.

“In order for us to be together, we needed you two not to get married. And if neither of you ever got divorced in the first place, you’d never need to marry each other. We wanted a parallel world that would fit the bill. So we climbed into the pod together…and we shifted.”

They exchanged another glance, and this time, they were frowning.

“You shifted? How? The machine is incomplete. It wasn’t even powered on!”

“I don’t know! Shiori and I just prayed to go to a world where you guys never got divorced, and it worked!” I yelled.

“You just prayed, and it worked? You shifted to a parallel world?”

“Yeah. That same method worked for me once before, actually.”

“…That time we found Shiori in the pod all those years ago?”

“Technically, it was right before that. Anyway, yeah, we repeated that same process, and…well, at the very least, I managed to shift. I made it to a world where you and Mom weren’t divorced, so I was gonna look for Shiori to see if she was there, but…then suddenly I was back here, and she was there in the pod with me, but…she wasn’t breathing…”

“What happened to her?”

“I don’t know… I swear…”

That was honestly everything I knew. I had no way of knowing what had happened to Shiori while I was in that other world. Neither the director nor my dad was angry with me, but truthfully, that only made it worse. Yell at me, damn it! Hit me! Tell me how to fix this!

The next day, Shiori was moved to Kyushu University Hospital. The director supposedly had a lot of connections there. She entrusted the ISRI to my dad and flew off to Fukuoka to be with her daughter. She wouldn’t let me tag along either; instead, she convinced me to stay home by assuring me she’d keep us posted. I obviously couldn’t say no to her.

True to her word, she updated us on the situation right away.

And that was how, through my dad, I found out that Shiori was brain-dead.

At the time, I didn’t know anything about the condition, but the implications of the term were more than enough to fill me with despair. Then, I heard that patients who experienced brain death were all but guaranteed never to wake up again.

That was the day my world lost its color. All at once, Shiori was gone, and so was my life’s meaning.

***

After that, I trudged through life like an empty shell. I didn’t want to think about anything. I didn’t even know what I was supposed to think about. But it was painful to sit around at home alone, so I wandered around outside. I had no destination in mind—I was just unable to stay in one place.

As I found myself walking in the direction of the train station, my feet changed course to a spot I’d wanted to visit with Shiori during summer break.

Chuo-dori Avenue, the main arterial, ran north from the train station, and after a ten-minute walk, it intersected with Showa-dori Street running east and west. This was the biggest intersection in our whole city. The southwest corner boasted a patch of greenery and a bronze statue called the Leotard Girl.

As I waited there for the crosswalk light to turn green, however, I thought to myself, Why bother? Why not just walk into traffic while the light was still red? That way, I could see Shiori again.

Supposedly, her heart was still beating—or more accurately, it was forced to beat through the power of medical technology. So she wasn’t dead yet, technically. But at the same time, I was told there was basically a zero percent chance that she would ever wake up again. So what difference did it make? Either way, Shiori was no longer a part of my world…and I had directly contributed to that.

I took an experimental step toward the street. A horn honked loudly, and I jumped back on reflex. Nope. I didn’t even have the courage to die.

After a while, the cars stopped coming; the traffic light on Showa-dori Street had turned red. That being said, the other traffic lights didn’t automatically turn green as a result. To prevent accidents, there was a recurring point at which every light at this intersection was red at the same time.

But during that brief moment when no one was supposed to be on the street, out on the crosswalk that by all accounts should have been empty…I saw a fuzzy patch of space.

Was I just seeing things? No, it was real. Something—someone—was right there on the crosswalk.

That was when I saw her.

A girl my age, with long black hair cascading over her white dress, faded into view.

A girl I recognized.

“…Shiori…?”

At that, the translucent girl looked up suddenly.

“Koyomi-kun…”

Her voice seemed to echo in my head. I recognized it immediately.

“I’m sorry, but…I guess I’m a ghost now.”

Interlude

Interlude

IWAS STANDING in the middle of a crosswalk.

My eyes, having adapted to darkness, were blinded by the sudden light of the city. One second, I was in a place so quiet we could hear each other’s breaths, and the next, my eardrums were painfully overwhelmed by car engines and footsteps.

Reflexively, I hunched into myself and covered my ears for a few seconds. Then, slowly, I looked up. I was standing in the middle of a crosswalk. A big one, and one I recognized all too well. It was the Showa-dori intersection, the largest in town.

What was I doing here? Wasn’t I just somewhere else, doing something else? Someplace dark and cramped…? Confused, I looked around.

Two or three people were running to the end of the crosswalk. Past them, I could see two figures standing side by side, looking over their shoulders at me. One of them was my mom, and the other…

“Dad!” I shouted before I could stop myself.

After that fiery divorce, my parents surely never saw each other again, and yet there they were, looking back at me like two peas in a pod. This was simply not possible…in my world, at least.

But then I remembered. I was trying to shift to a world where it was possible. And I succeeded! I really did shift to a world where my parents never divorced!

We gazed at each other across the crosswalk. Why were we so far apart? Wasn’t I walking with them? Oh, wait, I get it. When I first shifted here, it was a lot to take in, so I must have stood here for a while to process. But my parents didn’t notice, so they kept on walking without me, only to later realize I was missing.

Mom was looking at me with concern—and so was Dad, which made me really happy. In this world, they really were still together…which meant that in this world, Koyomi-kun and I were free to get married!

Gleefully, I started running across the crosswalk to catch up with them. Their expressions shifted, and they started beckoning to me. My ears hadn’t quite adapted, and my brain couldn’t process the sounds. I was solely focused on the sight of my parents together at last.

But by the time I finally perceived the red crosswalk light and the blaring car horns, it was too late. The cars came barreling toward me.

My brain must have processed it all in a fraction of a second. In that tiny moment, I thought about what would happen to me.

I’m gonna get hit by a car! I could die? I gotta run! But I won’t make it! What do I do? WHAT DO I DO?!

Just then, Koyomi-kun’s face rose to mind.

That’s it! Parallel shift! I’ll shift away before I get hit! To a different world! Please shift, please shift, please shift—

***

The next thing I knew, I was once again standing in the middle of the crosswalk.

But just when I thought I was safe, I saw the cars rushing at me all over again.

I’m gonna die!

I crouched down on the spot, shielded my head with my arms, squeezed my eyes shut, and waited. And waited. But no impact ever came…yet I could hear the cars whizzing past me. What was going on?

Timidly, I opened my eyes. The next thing I saw was a car bumper right in front of my face. Reflexively, I dropped back into position and closed my eyes—but like before, there was no impact.

As I crouched there, the car sounds faded out, and I heard the familiar crosswalk melody—the one that played whenever the crosswalk light was green. Now I could hear footsteps passing me by, so I stood up and slowly opened my eyes again.

The crosswalk light was green, and pedestrians were crossing the street. The traffic light was red, and the cars were stopped. I couldn’t feel any pain.

I struggled to process what had happened. Could it be that the cars all went out of their way to drive around me? It couldn’t be…could it?

As I mulled it over, I saw a group of people walking toward me. Instinctively, I tried to move out of their way, but…I couldn’t feel the ground under my feet.

Distracted by the strange (lack of) sensation, I realized in the next instant that the approaching group was about to crash straight into me.

Then I watched as they…passedthrough my body…and carried on walking like nothing ever happened.

“…Huh?”

I stood there, staring blankly, as the pedestrians bumped into me one after another. Except…none of them “bumped” me at all. They overlapped with me, passed through me, and walked on to the other side of the street.

Like I wasn’t even there.

Horrified, I looked down at my hands.

“What…?!”

My hands—no, not just my hands; my arms, my legs, my whole body was translucent. Light and sound…and people…could pass straight through me.

That was how I became the Showa-dori crosswalk ghost.

Chapter 3: Adolescence, Part 2

Chapter 3:
Adolescence, Part 2

“IMAGINARY KARYOMITOSIS.” The director read out the words she’d written, then rapped her knuckles against the whiteboard. “This is the tentative name I’ve given to my daughter’s condition.”

I listened attentively, unwilling to miss a single word.

My dad brought me to the lab with him this morning, and after we arrived, we holed up in a meeting room with the director, newly returned from Fukuoka.

A month had now passed since Shiori was confirmed brain-dead. In that time, the director had traveled back and forth between the ISRI and Kyushu University Hospital, and on some occasions, my dad went with her. I, too, was sometimes summoned to one of those two locations, and as a “sample” who had two different experiences parallel shifting to distant worlds, I was subjected to a lot of tests.

But…I wasn’t permitted to see Shiori, not even once.

Dad kept me updated on her condition, but it was always the same thing: There was no change to her current state. Every time. I was too stubborn to accept it, so I started doing some research on brain death. It only pushed me further into despair.

Unlike a vegetative state where the brain was functional enough to keep the body breathing on its own, brain death meant the brain had fully shut down—there was no regulatory function and virtually no chance of recovery. Most patients diagnosed with brain death would die within the week.

What if Shiori had actually died a long time ago? What if my dad and the director were just hiding it from me?

I was so frustrated that I wanted to just scream. Sometimes I did scream. I had no appetite, and whenever I wasn’t being overly combative for no reason, I was depressed to the point of contemplating suicide so I could be with Shiori again. But actually killing myself was too much effort—I simply wished I could stop breathing.

Naturally, given my current mental state, I didn’t go back to school when summer break ended. Instead, I spent my days at home, at the lab, or at the hospital in Fukuoka. The one silver lining was the kindness I was shown by everyone around me. That was the only thing keeping me sane. Other than that, I was living like a shut-in.

But then, just a few days ago, the director summoned me to the lab. She said she wanted to discuss something important with me. Only one topic could possibly fit the bill: Shiori. And so, scraping together the last dregs of my sanity, I came here today to listen to her speak.

“Firstly, Koyomi-kun, you should know that Shiori’s heart is still beating. The ventilator is preventing cardiac arrest.” The director had switched to her “professor” voice, as she always did when she was having a serious conversation.

“Is she still alive?” I asked.

“That’s a difficult question to answer. Her brainstem is alive, so she still has spinal reflexes, thermoregulation, fluid secretion, and so on. But her brain itself has lost all function—no voluntary movement, no senses, no thoughts, no memories, no emotions. And once a brain dies, it generally doesn’t come back. So whether or not we can say she’s alive is solely up to individual interpretation.”

In other words, her body was alive, but her soul was dead.

“But…they say most brain-dead patients die for real within a week…”

“Been studying, have you? In most cases, yes, that’s correct. But there are a handful of cases where the patient lived beyond that first week. One particular study showed that over the past thirty years, cases of ‘long-term’ brain death have numbered in the triple digits, and of those, seven survived for over six months. Some were kept on ventilators outside the hospital, and the one who survived the longest made it fourteen and a half years. In fact, at the time the study was written, that patient was still alive.”

“So you’re saying Shiori’s okay for right now?”

“I handpicked a team of competent medical professionals to keep her alive using state-of-the-art technology. They won’t let her die without a fight.”

This filled me with some sense of relief, not that we were by any means out of the woods yet.

“Getting back on topic… Patients with complete loss of brain function, like Shiori, are generally considered to have suffered ‘total brain failure,’ but I’ve decided to give her current state a different name.”

“Imaginary karyomitosis?”

“Correct. Brain death is normally the result of a car accident or severe illness that damages the brain beyond repair. But in this case, despite a thorough examination, we were unable to detect any injury to her brain. It simply stopped functioning.”

It made sense that her brain wasn’t injured. After all, she hadn’t been hit by a car in our world. Her physical body was safe in a pod the whole time.

“So why, then, did her brain stop functioning? I posit that it’s connected to parallel shifting,” she said.

At last, the director broached the main topic. The part that I was probably—no, definitely—partially responsible for.

“Twice now you’ve used the Cradle of Einzwach to parallel shift. One of those times was, of course, the most recent attempt with Shiori.”

“Einz-what now?”

“Don’t worry about it. It’s something I borrowed from one of my favorite old books.”

Come to think of it, Dad told me the director was a big fan of vintage manga, anime, novels, and video games. Supposedly, it helped inspire her thought process for imaginary science and parallel worlds.

“To my understanding, at the very least, that machine is still unfinished. And both times you used it, it wasn’t even powered on. So how did you succeed in shifting?”

I had no way of knowing. Instead, I remained silent, prompting her to continue.

“For the most part, parallel shifts occur naturally. We regularly shift to nearby worlds and back again without ever realizing. The slight differences between worlds cause us to ‘misremember’ those same details later on.”

So far, she hadn’t said anything that I, and by extension society at large, hadn’t already grasped.

“But the farther away a given world, the harder it is to shift to it naturally. During your first long-distance shift, you went to a world where your grandfather had passed away; the second time, you went to a world where Hidaka-kun and Takasaki-san were still married. Both must have been a considerable distance away, yet you succeeded in shifting there all the same. And not only that, but they were both worlds you consciously wanted to shift to. Voluntary parallel shifting is one of the very things I seek to research.”

At that point, I was starting to feel like some kind of superhuman freak. That had to be why they subjected me to all those confusing examinations this past month.

“This is still just a theory, but…I suspect parallel shifts are easier for some people,” she explained.

People like me, in other words?

“Koyomi-kun, do you understand why parallel shifts happen to begin with?”

“No…”

“I see. Hidaka-kun, you could have explained it to him, you know,” she remarked to my dad, who had thus far remained silent.

“I was going to, but then he stopped coming to the lab… Then again, I guess that’s my fault…” He was referring to the time he and the director questioned Shiori and me about the nature of our relationship.

“Right… I’m partially to blame for that as well. We need to do better, Hidaka-kun. We’ve spent so much time reading books that we’ve forgotten how to read people.”

“So it seems… I’m sorry, Koyomi,” my father said to me.

I didn’t know how to respond to their apologies. After all, I was most likely the root cause of what had happened to Shiori.

“In order to more easily explain the concepts of imaginary science, I devised the ‘Sea and Bubbles of Einzwach’ model. As you know, it’s an analogy that likens imaginary space to the ocean and our world of origin to a single bubble born on the ocean floor, with a vertical axis of time. The bubble rises toward the top of the Sea of Einzwach, growing and splitting off into infinite parallel worlds.”

This was the first concept of imaginary science that my dad had ever taught me, so I grasped it quickly.

“Fundamentally speaking, there are macro-bubbles and micro-bubbles. Put simply, macro-bubbles represent entire worlds, while micro-bubbles represent the individuals within them. Now, there’s a sort of intermolecular force between these bubbles, and the inertial force produced by the motion of a macro-bubble can knock other bubbles into each other, causing them to switch places. If the bubbles are close in proximity, they’ll revert quickly, but if the bubble is somehow sent flying a considerable distance, it’ll take time before they revert.”

In other words, this was the concept of parallel shifting, but with bubbles.

“Mind you, this theory is still incomplete, but…perhaps twin bubbles are tied to each other, making it easier for them to slip out of the macro-bubbles. Let’s say their imaginary density is high, or something. These bubbles have a powerful will to change. So when these individuals wish strongly to travel to another world, the imaginary elements react with a parallel shift.”

“And you’re saying I’m one of them?”

“In theory.”

If so, would I be able to help that pod—the Cradle of Einzwach—reach completion?

“Um, I have a question…” I started.

“What is it?”

“Imaginary elements give form to physical matter, right?”

“Yes.”

“Conversely, all physical matter is composed of imaginary elements, right?”

“That’s right.”

“Does that mean pencils, and notebooks, and…and rocks or whatever…can all parallel shift too?”

“Precisely. That said, our worlds are basically never impacted when it happens. After all, the only thing that shifts is the imaginary; the physical remains in place. In short, for human beings, what switches places is our souls, but objects don’t have souls, so nothing really changes. Technically speaking, there is an infinitesimally small chance that it could influence something, but that influence would also be infinitesimally small.”

“Ah, I get it.” The chair I was sitting on could be parallel shifting right this instant, but nothing would change as a result.

“Make sense? Then let’s get down to brass tacks.”

Again, the director smacked the whiteboard. Oh, right. That was all just preamble for the main topic.

“Tell me, what would happen if a micro-bubble popped while in transit between macro-bubbles?”

If the macro-bubbles were parallel worlds, and the micro-bubble was a person, and they “popped” while in transit…

“They would…die?”

“No. The bubble’s imaginary element would be dissociated from the physical form it was substantiating.”

This time I didn’t need an analogy. After all, I had witnessed this concept with my own two eyes. The rest of this conversation simply served to more easily explain what had happened to her.

“So that’s imaginary karyomitosis?”

“Yes. After examining you and Shiori and hearing your side of the story, in addition to what Shiori’s ghost told you, this is the conclusion I’ve reached.”

I had already told her and my dad everything Shiori’s ghost had told me at the Showa-dori intersection: that in the split-second when she was about to be hit by a car, she tried to parallel shift to escape, and the next instant, she was turned into a ghost.

“Inside the Cradle with you, her imaginary elements were pulled along with yours into a parallel shift. And on the other side, at the precise moment she was hit by a car, she tried to shift again, to a world where she wasn’t in danger.”

She must have believed she could escape from it. After all, we were already trying to escape from something else.

“As a result, her micro-bubble flew out of the macro-bubble, and right as it was crossing the Sea of Einzwach, it burst. Her parallel self likely died instantly. But parallel shifts work by trading places, so once her other self was unable to return to her original body, so too was our Shiori. Her imaginary elements were left suspended in the Sea of Einzwach, and with no physical form, she was turned into a ghost at that very crosswalk.”

I couldn’t pretend I understood everything she said, but what I did understand was that I most certainly had a hand in this happening.

“Is there any way to save her?” I asked the director.

“…If my line of thinking is correct, we would need to pinpoint her imaginary elements in the Sea of Einzwach, find a way to control them, then attach them back to her physical body. That said, we still don’t have a method of observation. As imaginary science progresses, I suspect these things will eventually be possible, but realistically speaking…I doubt Shiori’s body could last that long.”

We were out of options. Only a literal god could save her at this point. How could this have happened to us? All we ever wanted was to be happy!

“It’s not your fault, Koyomi-kun,” the director said suddenly, switching out of professor mode. I must have let the despair show on my face.

This woman had every right to blame me for her daughter’s condition. It was my fault Shiori was a ghost now. Why couldn’t she insult me and punch me like I deserved? Her sympathy sent me flying into a rage.

“How can you be so calm about this? How can you keep a level head while your daughter’s on a ventilator?! All this stupid technobabble won’t even save her! So why won’t you just blame me already?! Aren’t you sad?! What kind of mother are you?!”

I knew I was being cruel, but I couldn’t stop myself. All my feelings—my love for Shiori, the guilt of being unable to save her, anger at my own worthlessness, frustration with the adults’ inexplicable composure, and most of all, the gut-wrenching horror I felt thinking about her ghost being left all alone at that crosswalk—all of it had melted together into a sludge. I needed to get it out of my system before I truly went insane.

“None of this would have happened if you two hadn’t gotten divorced! That way, Shiori and I could have been together!”

Like a total hypocrite, I blamed it on them instead of my own ignorance. Neither of them said a word, as if to suggest they had no defense. Logically, at least one of those divorces was what introduced me to Shiori in the first place, but I was too emotional to think that far.

“…I concede that perhaps people like us had no business getting married,” the director said in a small voice. My dad simply frowned. “But let me say this, Koyomi-kun.” She looked directly into my eyes and finished her thought. “Of course I’m sad, you imbecile.”

Her expression remained unchanged as a single tear rolled down her cheek—and I snapped back to my senses. I was being so childish. What was I thinking? There was no way on earth she wasn’t upset! Who the hell did I think I was, attacking a woman who had lost her only daughter?

I had done the unthinkable, but I didn’t know how to own up to it. What was I to do? Right now, I had only two words to offer.

“…I’m sorry.”

“It’s all right. Likewise, I apologize for calling you an imbecile. What I meant was, it’s not solely your fault. If anything, the part you played in this was the smallest of all. You didn’t force her to make the choices she made.”

She wiped her tear with her lab coat sleeve and carried on like nothing was wrong. That said, I couldn’t just let bygones be bygones and go back to my life. If there was anything I could do to help Shiori, I was going to do it.

“Director, Shiori has a spare key to the Cradle room.”

“I know. She probably had it made in secret and used it to sneak in with you that night, didn’t she? That makes it even less your fault.”

“Can I have it?”

Her eyes narrowed at me. “For what purpose?”

“So I can use the Cradle. I’m going to comb through the other worlds and search for a way to save Shiori. After all, shifting is easier for me, right?”

Sure, maybe the Cradle wasn’t finished, but Ihad the ability to use it, regardless. All I had to do was parallel shift through each and every world until I found one where Shiori was cured, ask them how they did it, then come home.

“You could do that, but I don’t think you should. We don’t know how dangerous it might be. Besides, there’s a chance you’ll suffer imaginary karyomitosis yourself.”

“I don’t care. I want to help Shiori.”

“Well, I do care!” she countered. “Didn’t I just tell you? I’m not an unfeeling monster. Besides, if something happened to you, your father would be devastated.”

At this, I looked at my dad. He remained quiet and still, just as he’d been the whole time I was ranting at them. To be honest, I still couldn’t quite understand what he was thinking, but we’d lived together for years and years now. And besides, we were both…

I looked straight into his eyes and summoned all my emotions—all my courage. Likewise, he gazed straight back at me. And then, without a word, we nodded at each other.

“Director, could you let Koyomi have the spare key?” he asked.

“Hidaka-kun…? What are you saying?”

“When a man loves a woman, he’ll do whatever it takes for her. There’s nothing we can do to stop him.”

And then my father, of all people, gave me a thumbs-up. Tickled, I gave him one right back. I knew he would understand. We were both guys, after all.

“Well, that’s not fair. I can hardly argue with that, now can I?” the director sighed as she watched our exchange. Then she smiled wryly. “Fine, you win.”

“Thank you so much!”

“But under one condition: you must always report to me or your father whenever you want to use the Cradle. All of your shifts will be monitored and recorded.”

“Okay!” Then I paused for a moment. “Wait, but doesn’t that defeat the purpose of me having a spare key?”

“Just take it anyway. Here.”

“Huh?”

The director fished something out of her pocket and handed it to me. Sure enough, it was the same key.

“You had it with you…?”

“I found it when I was sorting through Shiori’s belongings. Technically, it’s company property, so I was thinking of keeping it at home just in case, but…you should hold on to it.”

“…Okay.”

Now that I thought about it, right from the day we first met, Shiori was always more passionate about parallel worlds than I was. She wanted to travel to a world where her parents were still together, but she was too scared to get in the Cradle by herself. That was why she used me as a guinea pig. What a crazy way to meet someone for the first time.

As I recalled her face and voice, I gripped the key in my palm. One day, this key would open the door to a happy future with her. I just needed to have faith.

***

Starting the very next day, I began a new daily routine: I went to school during the day, and then did experiments at the ISRI at night.

I decided to go back to school because I had learned that ignorance was a cardinal sin that could destroy everything. Plus, I was now serious about pursuing imaginary science as a career. If I did, surely I’d be able to help save Shiori. After all my time at the lab over the years, I was primed to absorb knowledge, and my grades swiftly shot back up.

My first parallel shift experiment under the supervision of my dad and the director took place during the winter of my second year of junior high. We had agreed to start with nearby worlds, so I climbed into the powered-on Cradle, closed my eyes, and prayed to go to the parallel world next door.

A few seconds later, I opened my eyes and found myself still inside the Cradle. I could see Dad and the director peering in at me through the glass. Then they opened the door, and I sat up.

“Did it work?” the director asked me, but I didn’t know how to answer. After all, nothing had changed from a few seconds prior. Neighboring parallel worlds had only the most trifling of differences, like what you ate for breakfast. Now that I thought about it, how was I even supposed to make sure I was in another world? Evidently, this conundrum convinced the director to speed up development of the IP bands that could identify which world the wearer was in.

That said, even if I succeeded at shifting, it didn’t mean anything. The neighboring worlds were so similar that their Shioris were all ghosts too. Ultimately, the only thing I gained from that first experiment was the knowledge that nearby worlds were worthless.

***

In the beginning, the experiments happened every two or three months. The adults wouldn’t let me schedule more than that; instead, they kept subjecting me to confusing tests that measured all sorts of numerical values. Since they told me it would further the progress of imaginary science as a whole, I couldn’t possibly decline.

The second parallel shift experiment happened three months after the first. This time I traveled to a world five doors down from ours. But once again, there were barely any changes. I could tell it was a parallel world because everyone was wearing different clothes, but Shiori was still a ghost there.

Just in case, I decided I would speak to this parallel Shiori. I headed to the intersection and sure enough, there she was, wearing the same smile as my Shiori did.

“Oh, Koyomi-kun! Hi!”

But was she the same girl I knew?

“Hi, Shiori. I’m actually from a parallel world.”

“What? Really?”

“Do I seem any different from the me you know?”

“Ummm… I can’t tell. You look the exact same.”

Hearing it put so bluntly was like a punch to the gut, since I liked to think of myself as unique and my parallel selves as totally different guys. That said, I had no right to complain when I couldn’t tell the difference between this Shiori and the one back home. Feeling guilty, I went back to my home world and visited my Shiori next.

“I’m here, Shiori.”

A nearly transparent Shiori smiled back weakly from the crosswalk. “Oh… Koyomi-kun. Thanks for coming. It means a lot.”

She was located just two or three steps away from the street corner, so I always stood at the very edge of the sidewalk to talk to her. That was the spot where she got hit by a car. If only she’d had enough time for two or three more steps, she could have lived.

“I did a parallel shift for the first time in ages yesterday.”

“Yeah? How’d it go?”

“Sorry… I still couldn’t find a way to save you. But I’m gonna find it, I promise. I’m gonna rescue you.”

“I know. Thanks.”

At times like these, it felt like Shiori was really there. But then the lights would change, and the cars would start rolling through her. Once the lights changed again and the pedestrians all walked off, I spoke up once more.

“Has anything changed for you?”

“Well… Ever since yesterday, these two pigeons have started coming by the Leotard Girl. I think they might be mates.”

She acted like nothing was wrong, but I could only imagine how miserable and lonely it was to be trapped in the same spot for eternity. I wished I could live full time at the intersection because the sight of her pained smile as she waved goodbye broke my heart every time.

And so I went to the intersection nearly every day, waited until the street corner was deserted, then spoke to her.

That said, I couldn’t avoid the public eye every single time. And not only that, but bizarrely enough, I was the only one who could actually see Shiori. No one else on the street could see her, not even my dad or the director. Because of that, the passersby all gave me a wide berth like I was crazy. But I didn’t care. Shiori mattered more.

She told me that every now and then, someone would notice her and get spooked. It probably had something to do with whether someone had a “sixth sense” or not. Or maybe it had to do with imaginary density, like with my heightened aptitude for shifting. Regardless, my life now consisted of studying, experimenting, and talking to a ghost.

***

The third parallel shift experiment took place in May, right after I started my third year of junior high. Convinced there was no point in visiting nearby worlds, I decided to shoot for the stars and prayed to shift 50 worlds away. The next thing I knew, I was in a room I didn’t recognize.

The worlds near mine were all doing the same experiments, so my parallel selves were all shifting at the same time. As a result, I would always find myself inside the Cradle when I arrived. But this time, for the first time, I was somewhere else. This parallel me wasn’t doing any experiments. Could that mean…the experiments weren’t necessary? Because Shiori wasn’t a ghost here…?

First things first, I needed to figure out where I was. Our experiments were conducted late at night to prevent any more tragic accidents. When I pulled out my phone, sure enough, I saw that it was 1 a.m. Then I checked my contacts, just in case, but Shiori’s name wasn’t listed.

Quietly, I slipped out of the room. The house was dark—no surprise there, given the time of night. Using my cell phone light to illuminate my path, I searched the unfamiliar house.

Arriving in the living room, I began digging around for clues wherever I could. But suddenly, the lights clicked on. Startled, I whirled around to find my dad…standing there with my mom.

“Koyomi? What are you doing this late at night?”

In his right hand was the wooden sword I’d bought as a souvenir during one of my school trips. He must have heard something and thought it was a burglar. (Now that I thought about it, it was pretty shady of me to go snooping through the house with all the lights off.) As for his left arm, my mom was clinging to it in fear. They looked so natural together that I could tell they weren’t divorced in this world.

“Koyomi…? What’s the matter, sweetie?”

Mom must have got worried when I didn’t answer, because she let go of Dad’s arm and walked over. I didn’t have time for this, however.

In a world this distant from mine, Shiori might still be alive. I wanted to see her. That was all I could think about. But her name wasn’t in my phone, so that meant this parallel self hadn’t even met her.

“Dad! Could you introduce me to the director’s daughter?!”

The sudden request left him utterly perplexed. “Where is this coming from…?”

“C’mon, the lab director has a daughter who’s the same age as me, right? I want to meet her!” I insisted.

“Well, yes, she does… Now explain why.”

I wasn’t that opposed to explaining it to him in theory, but right now, I didn’t have the composure to go through all the finer details with him. I just tossed out the first excuse I could think of. “I saw her in passing at the lab the other day and fell in love with her at first sight!”

Dad’s expression went hard; conversely, Mom broke out into a smile. “Well, well, well! I suppose you’re getting to that age, aren’t you, Koyomi? Were you searching the house to find her address or something?” she asked.

“Huh? Oh… Uh…y-yeah. Sorry I scared you.”

“Oh, that’s fine, honey! But you can’t just show up at her door unannounced. Daddy, do him a favor and play matchmaker, won’t you?”

“Huh? Oh…er… Y-yes, dear. Sure, I don’t mind.”

And so, with my (parallel) mom’s help, I met Shiori in that same world the next weekend. But the Shiori I met…

“Um… Nice to meet you. I’m…Satou Shiori.” She was guarded, like I was some kind of threat.

This isn’t her, I thought to myself. She was the same person, sure, but she was totally different. This Shiori wasn’t the girl I fell in love with. Worlds with a living Shiori that had never met me wouldn’t help me with my mission.

No, to save my Shiori, I needed a world with a living Shiori that already knew me. Otherwise, it was all pointless.

***

After I explained everything to my parallel dad and convinced him to let me use the Cradle to come back home, my actual dad and the director yelled at me for traveling to a distant world without their permission. Then, they told me how happy they were to have me back.

As for me, however, I developed some severe anxiety. Was I truly back home where I belonged? Was this the same world I originally departed from? There was no proof anywhere. How could I be sure this wasn’t the world next door? And not only that, but what if Dad or the director had shifted from another world themselves?

Any further experiments were suspended for a while due to my mental instability.

Nevertheless, I continued to meet up with Shiori. According to her mom, her imaginary elements were fixed in place the moment she became a ghost, and therefore she was unable to parallel shift in her state. Add in the fact that most people shifted naturally about once a day on average, and Shiori was the one person I felt it was safe to talk to.

Meanwhile, the director became so concerned about my condition that she made the development of IP bands her number one priority. As a result, a prototype was ready before I even graduated junior high, and it was decided that I would be its first tester. Once it registered my home world as World Zero, it would measure the IP variation and display what numbered world I was currently in. Wearing it truly did wonders for my anxiety, so I jumped back into parallel shift experiments with increasing frequency.

From there, I used the Cradle to parallel shift about a dozen times. All of the worlds were relatively close. In all of them, I had chosen to live with my father after his divorce and met Shiori at the lab…and in all of them, she was now a ghost.

Going back to the bubble analogy, micro-bubbles were often referred to as “twins,” but of course there were more than just two of them. All bubbles who split off from each other were considered twins. Putting it simply, in the majority of these nearby parallel worlds, Shiori had suffered the same accident.

But I had only shifted a dozen or so times, and the worlds were limitless. Surely there had to be a world where Shiori had been saved, or so I told myself.

But deep down, I couldn’t help but wonder… Was this what they called “fate”? Or was it a curse inflicted upon her the moment she met me?

***

At age seventeen, Shiori was taken out of the Kyushu University Hospital and put on a ventilator in a newly constructed room for her at the Imaginary Science Research Institute. The director had it remodeled into a living space so she could be with her daughter at all hours of the day and night. As for me, I kept combing the parallel worlds for a way to save her. But, as I had feared, I still had yet to find it.

Meanwhile, I continued to study my ass off until I was accepted as the incoming first-year valedictorian at the most competitive high school in the entire prefecture. The first thing I did was go to the lab and tell Shiori’s body; then, I went to the intersection and told her ghost. She jumped for joy and told me she was proud of me. That was what just barely kept my soul from breaking down.

But then the day finally came…

“Koyomi.”

One cold winter day, I was about to leave for school, but my father stopped me.

“No school today. You’re coming with me to the lab.”

It was the first time he ever wanted me to cut class in favor of the lab, so I knew it had to be important. Maybe Shiori was showing signs of recovery! I tried not to get my hopes up, but deep down, I just couldn’t help myself.

Dad brought me to Shiori’s life-support room.

“Oh, hello. Thank you for coming, Koyomi-kun… Come on in,” the director said, greeting us.

Her eyes were red, which was uncommon for her. Had she pulled an all-nighter? Regardless, I didn’t have the mental bandwidth to worry about her. If they were making me skip school to be here, then there had to be some kind of good news. I ignored the sense of gloom I sensed from the adults and went straight to Shiori’s side.

She was still lying there on her bed…but she had been taken off the life support machinery.

“…Shiori…?”

I stroked her ghostly pale cheek…and I felt the same lack of warmth that she and Yuno had taught me as a child.

“About an hour ago…her heart stopped beating.”

A single thought crossed my mind. I wish mine would too.

***

After a modest funeral, I watched the smoke rise from Shiori’s cremation. In place of funeral attire, I was still wearing my school uniform. Then, I went to the intersection, where Shiori’s eternally fourteen-year-old ghost greeted me with a smile.

“Hi, Koyomi-kun. Long time no see.”

“Yeah… Sorry.”

Normally, I visited her daily without fail, but I had left her on her own for the past three days. I just didn’t know how I was supposed to tell her that her body had left this world for good.

“Did something sad happen?” she asked me gently. When I didn’t answer, she continued talking. “It’s okay, Koyomi-kun. Don’t cry. I’m here for you.”

Her translucent hand attempted to stroke my hair, but it passed right through me. Then, the light changed, and pedestrians started walking by. Whole crowds of people walked past us…and not one of them even noticed Shiori was there.

Interlude

Interlude

AFTER SHIORI became a crosswalk ghost, the field of imaginary science progressed at an astounding rate. One of its global achievements was the IP band the director had been focused on—a wristband device that could display, in numbers, what world the wearer was currently in by measuring its Imaginary Elements Print. Once the prototype was complete, tests were performed at laboratories all over the world, and a few years later, even ordinary citizens were enlisted to test them out.

The ISRI’s research had taken a big step forward as well in terms of my dad’s main focus: IP stabilization. This research involved observing imaginary elements overlaid in an imaginary space, then freezing the quantum state and preventing any flux. Were we to achieve this, we would then be able to prevent parallel shifts, or so the theory went. If this technology could be made widely available, we’d be able to prevent all sorts of accidents, such as those caused by shifting while driving, among others. Humankind needed this technology if we were going to embrace parallel worlds as a part of our everyday lives. That said, we still hadn’t found a way to directly observe imaginary elements, which remained the key to our research.

Last but not least, progress had also been made on the Cradle of Einzwach, the device used for parallel shifting at will. All the data they gathered from my trips must have contributed a lot. But of course, because it counted as human experimentation (and on a minor, no less), the only people who knew about it were me, Dad, and the director.

She christened this new, voluntary type of shifting as “optional shifting” and made it the lab’s main goal to find a practical application for it within the next twenty years. If we could finalize this tech, we could possibly share information between parallel worlds concurrently, and at that point, not just imaginary science, but all fields of civilization were predicted to make great progress.

In contrast with the stellar outlook for imaginary science, however, my personal life quickly soured. After Shiori’s body was taken from the world, the only emotional support I had left was her ghost.

Originally, I was planning to graduate high school and enroll at Kyushu University Faculty of Science, Department of Imaginary Science. It was at Kyushu U’s physics department that our director first started independently researching imaginary science. From there, she transferred to a graduate school in Germany, and finally came back to Japan and became the country’s youngest professor. With financial backing from her hometown, she then established the Imaginary Science Research Institute, of which my father was a co-founder, and the rest is history.

Back when I was ten years old, she first announced she had proven the existence of parallel worlds at a scientific conference. In a blink, imaginary science became its own field of study, and “that weird laboratory in Nowhere City” became a household name around the world. In response, Kyushu University added a Department of Imaginary Science to its Faculty of Science. A handful of researchers, including the director, were invited to teach there part-time, and Kyushu U quickly became the number one school for imaginary science—not just in Japan, but in the world.

In the beginning, my plan was to study imaginary science there, then come home and research how to save Shiori. But when her body died, it was all over for me. Attending that school would’ve required me to move to Fukuoka, leaving her ghost at the intersection all alone. I couldn’t abandon her. It would be too cruel.

Instead, I dropped out of high school and got a job at the lab. I wasn’t even remotely qualified, of course; I was a total nepotism hire. But Dad and the director sympathized with me—perhaps a bit too much, honestly—and all the other researchers had known me since I was a kid. You could at least say I was a good cultural fit.

At eighteen, I started receiving a monthly salary as an official employee. After that, I moved out of Dad’s house and started living on my own. I could barely afford my living expenses, but I was fine scraping by. Then, I dug up the “remarriage” conversation that had gotten shelved after what happened to Shiori, and after a little nudging, Dad and the director got married the next year.

Granted, I didn’t do it because I wanted them to be happy. I mean, I did want that, obviously—but my biggest objective, more than anything, was to be alone. I wanted to think of nothing but Shiori, as much as possible; I wanted to devote all my free time to the intersection. That was why I needed my own place. Still, I had just enough humanity left in me to worry about my aging father being all on his own. Maybe they were so amenable to getting remarried because they could tell I felt that way too.

And so, with my newfound alone time, I visited the intersection every day to see Shiori. The only other thing I took seriously was my research. I hadn’t given up on saving her—I was still conducting optional shift experiments using the IP capsule (the official name for the pod the director previously called the Cradle of Einzwach), and I was starting to work my way toward long-distance shifts. But even after nearly a hundred experiments, every Shiori that had come into contact with me had succumbed to imaginary karyomitosis.

In more distant worlds, there were Shioris living happy lives that I had never been a part of, but I just couldn’t see those parallel Shioris as the same Shiori I loved. To me, there was only the one. And the more worlds I visited, the stronger this sentiment grew.

Around this time, I became obsessed with my “fate” theory, convinced that the act of meeting me had single-handedly ruined her life in every single world. After consulting my dad and the director, I started calling it the causality radius. If a given event happened in one world, it was all but guaranteed to happen in every world within a certain proximity. Conversely, the farther the world, the less likely it would happen. I wanted to quantify that radius.

Using the Sea of Einzwach model, the event in question would count as its own macro-bubble. Inside it, a micro-bubble with a specific outcome would split into parallel worlds, all trapped within the same causal set. Unable to escape, these worlds would all arrive at the same outcome, with no exceptions—or so my theory went.

With the lab’s help, my theory was proven, then promptly accepted as an official doctrine of imaginary science. Because the distance was measured by IP, the concept was formally named the Schwarzschild IP (SIP), referencing the term used to measure the radius of a black hole. (Incidentally, the director helped me name it, and I suspected she was once again inspired by some old piece of fiction.)

Once my theory was accepted, this young high school dropout started making a bit of a name for himself. But I had no interest in fame beyond the funding it helped me get for my research. I still had only one goal—to rescue my Shiori.

But oh, the irony. My SIP theory had just proven that there was no way to save her. Because, you see, my first encounter with Shiori was its own causal set. That meant that in every world therein, she had been turned into a ghost.

We still hadn’t established a method to directly observe imaginary elements, but even if we did and we could pinpoint precisely where her imaginary elements were stuck, we no longer had a physical form to attach them to. Her body had become ashes years ago. At this point, I could only think of one possible method with which to save her—and only one way to achieve it.

Parallel shifting, as the name would suggest, was a lateral transposal through imaginary space. But no amount of lateral movement would help me. If I wanted to get anywhere, I needed to move vertically.

In other words…time travel.

Chapter 4: Adulthood and Middle Age

Chapter 4:
Adulthood and Middle Age

IWAS TWENTY-SEVEN YEARS OLD when I was “reunited” with that woman.

She had graduated at the top of her class at Kyushu University Faculty of Science, Department of Imaginary Science, and in grad school, she presented her doctoral thesis at an academic conference to great acclaim. Then, she completed her PhD in record time, turned down postdoc fellowship offers from universities and laboratories in other countries, came back to her hometown, and applied to work at the ISRI. As it turned out, her father was one of our longtime researchers, and he gushed about how proud he was to anyone and everyone who would listen.

The whole lab was in a tizzy over this competent young candidate, my dad and the director included. But unless she was going to discover a way to save Shiori, I didn’t care. Naturally, it was unanimously agreed that she would join our team starting April 1.

The ISRI’s turnover was generally low, so she was the only person hired that year. As a result, there was no real “welcome party” held for her beyond an all-hands meeting where we introduced ourselves. Even then, attendance was optional, so I chose to spend that time on my research.

Later that day, Dad gave her a tour of the building to show her our facilities. Naturally, they came to my assigned room, and that was where I met her for the first time.

…Well, technically it wasn’t the first time. In actuality, it was the second, but I hadn’t put two and two together yet. I wasn’t interested in her, so I just bowed to her in silence without even making eye contact. The most I would give her was my name.

It was Dad who started the introduction. “This is Hidaka Koyomi-kun, senior researcher for this department. Full disclosure, he is my son, but there’s no need to give him special treatment.”

“Yes, sir.”

My first impression was that she seemed aloof. Behind her glasses, her almond-shaped eyes afforded her an air of icy intellect, and though she was face to face with a new colleague and possibly future boss, her expression was devoid of any forced pleasantries. To me, that wasn’t a bad thing whatsoever. All that mattered to me was her skill. Flattery would only waste time.

“Koyomi, this is that new hire I was telling you about. Not to lump all the young people in the same room, but I’m thinking of assigning her to you.”

To be quite honest, this offer came as a mixed blessing. I had been made “senior researcher” practically out of nowhere—there weren’t even any other researchers in this room with me—and now I was going to have a subordinate?

My isolation was partially due to being the youngest researcher on the team, but more than that, I simply produced better results working alone. That was, of course, intentional on my part; I didn’t want to build any unnecessary interpersonal relationships. In reality, I had spent the past ten-plus years thinking only of Shiori. The director seemed to be okay with that, but my dad probably couldn’t help but worry about me the way only a father could. He must have been planning to assign me a young new subordinate right from the start.

But…no one else knew that my current objective was to establish a method of time travel. I was using my parallel world research as camouflage. Of course, it was always possible that the field of imaginary science would arrive at time travel eventually, but currently it was believed that only lateral movement was possible.

Using the notebook analogy, you could move to different points on the same page, but to reach a different page would involve piercing through the paper—in this case, the “paper” would refer to imaginary elements. In other words, time travel would require breaking the barrier created by imaginary elements. And since imaginary elements gave form to physical matter, breaking that barrier would theoretically destroy the physical matter too.

In summary, the tenets of imaginary science dictated that time travel would equal the destruction of the world.

Because of that, none of us were researching time travel—or at least, we weren’t supposed to be. I was only being paid to research parallel worlds. And since I needed to reallocate that funding to my secret time travel research, having another pair of eyes in this room would only hinder me.

I contemplated all this in the span of a second while the new hire stepped forward to introduce herself.

“I’m Takigawa Kazune. Pleased to make your acquaintance.”

She bowed, then looked directly into my eyes, and suddenly…it felt as though I’d heard that name somewhere before. Had the researchers said her name aloud when they were reading off her resume? I had no memory of it. Had I seen her name when I skimmed her lauded doctoral thesis? Surely I’d remember if so.

Once more, I observed her face. Intellectual features, thick lenses, narrow eyes that exuded an unapproachable aura, light brown hair worn in a bob cut… Yes, I was convinced I’d seen her somewhere before.

After Shiori became a ghost, I stopped participating in most social interactions. I never had friends in high school, and after I dropped out, I only ever went to the lab, to the intersection, and then back home again. Was she a part-timer at some cafe I went to once? No, surely I wouldn’t recognize a random barista…

“You two may be the youngest researchers on our team, but you’re no less talented. Any field could stand to benefit from fresh, young eyes. I hope the two of you can work together to further the legacy of imaginary science,” my dad summarized neatly. In the blink of an eye, he was suddenly in his fifties, but he really shaped up over the years. And out of respect for him, I found myself acting like a normal human for once.

“Nice to meet you, Takigawa-san.”

I extended my hand, and she gripped it…hard.

***

It wasn’t until more than a year later that the mystery of where I’d first seen Takigawa-san was finally cleared up.

Just as everyone had hoped, she proved to be a truly talented researcher. During her initial trial period, she shadowed many different people for training purposes, but she absorbed it all quickly and sometimes even put forth suggestions for more efficient processes. Apparently, the director wanted to formally hire her right away, and after the higher-ups talked it out, sure enough, she was assigned to my research room. For the first time in my career, I was going to have a coworker.

Then, at the end of the workday…

“Koyomi, come here a second,” my dad called as I was walking past the break room.

“What is it?”

When I approached, he held out a single envelope. I took it and opened it to find two 10,000-yen bills inside.

“Need me to buy supplies or something?” I asked.

“No, I want you to use that money to take Takigawa-kun out to dinner tonight.”

“Excuse me?” I scowled.

“Starting today, you two are a team. You need to establish rapport with her.”

“Pass. Not necessary. I’m going home.”

“Now, now, hold on a minute. I’ve already put in a reservation at a restaurant your mother suggested,” he said.

“What the hell would you do that for? Just take Mom then!”

In this instance, “Mom” referred to the director. After the two of them got married, I made an effort to call her that in private…to stave off the guilt.

“Sorry, but she and I are going to a different restaurant tonight, so the reservation will go entirely to waste if you don’t make use of it.”

“Who are you and what have you done with my dad…?”

It felt like he was trying to play Cupid for his perpetually single son. At first I thought maybe he was worried about me now that he was getting on in years, but this quickly proved not to be the case.

“Look, I know you haven’t moved on from Shiori-chan,” he said suddenly, and my breath caught in my throat. “It’s your life, and I won’t criticize your choices. But at the very least, you should try to expand your possibilities. Takigawa-kun is a truly brilliant researcher, and I’m confident she can help you. It won’t hurt to establish an amicable relationship with her.”

“Are you seriously playing the Shiori card right now?”

“You were already thinking of Takigawa-kun as a potentially useful pawn, were you not? Well, she will be useful, make no mistake.”

Evidently, my father was still the same man he always was. Like me, he was missing some element of humanity deep down.

I paused before answering him. “Fine. I accept.”

I put the 20,000 yen in my wallet and saved the restaurant’s contact info in my phone. If the director picked the restaurant, then it’d hardly be any different from a work meeting. I sat there in the break room and waited for Takigawa-san to arrive.

As the reality set in, however, I started to get nervous. It had been more than a decade since my last social interaction, and other than Shiori, I didn’t have any experience inviting a woman somewhere. What was I supposed to say?

If I start with, “Great work today,” she’ll say, “Thanks, I’ll see you tomorrow,” and I’ll say, “Take care”… Gah, no! I can’t let her walk out! How about, “Great work today! Want to have dinner?” Ugh, too sudden. How the hell did I invite Shiori anywhere? “Let’s grab some grub”? Not happening…

The more I tried to think about it, the harder my heart throbbed. It had been so long since I last felt this tightness in my chest… It was kind of nice, but at the same time, I felt guilty. After all, Shiori would never get to feel her own heartbeat ever again… And it was all because I…

“Hidaka-san?”

My heart nearly stopped. “Oh, uh…hi, Takigawa-san.”

The next thing I knew, Takigawa-san was standing right in front of me. She must have finished her work. This was my chance to ask her to dinner. I just needed to follow the script I—wait, why was my mind blank all of a sudden? Wasn’t I just planning what to say?

“Great, uh…great work today…”

“Thanks. You too, Hidaka-san.”

I couldn’t think of what to say next. What was wrong with me? Why couldn’t I just talk to her like I could with Dad and Shiori? Had the past ten years of relative isolation completely robbed me of all communication skills? My heart pounded out of control, and I began to sweat. I wanted to say, “Let’s get dinner,” but my mouth suddenly couldn’t remember how to make L sounds.

Takigawa-san noticed my silence and frowned. “Erm, the vice-director told me you’d be taking me to dinner tonight…”

For the first time in ages, I felt sincerely grateful toward my father.

***

The restaurant was about a ten-minute walk from the train station—a gastropub on the first floor of a building on a side street in the arcade district. As we walked in, however, both of us started to frown.

“Is this the right place?”

“Well, it should be…”

Inside the building, the walls and corridors were plastered in anime and video game posters. What in the world was this place?

“What do you mean, it should be? Didn’t you make the reservation, Hidaka-san?”

“Uhhh… Actually, it was my father. He wants us to ‘establish rapport’ since we’ll be working as a team from now on.”

“I see… Wait, so the vice-director is into this sort of thing…?”

“I don’t think so… Oh, that’s right. He said the director suggested this restaurant.”

“She did…? Ah, that makes sense.”

Evidently, she understood without needing to be told directly. Admittedly, it was common knowledge in our sphere that Professor Satou, director of the ISRI, was what you’d call an otaku. Specifically, she was a fan of vintage manga, anime, light novels, and video games, and she had gone on record stating that her media consumption had influenced her thought process regarding imaginary science and parallel worlds. She even outright named some of them as “reference materials.”

“If she recommended it, then I suppose we’re obligated to try it…”

“Yeahhh… Welp, in we go.”

We passed under the sign that read OTAKITCHEN and pulled the sliding door open. The delicious smell of a gastropub wafted out to greet us, but my attention was immediately drawn to the décor. To no one’s surprise, every inch of the place was drowning in more posters and figurines.

“Welcome!”

“Hi, I have a reservation under Hidaka.”

“Ah yes, Hidaka-san! Right this way to your private room!”

We walked across the main floor to a sliding door on the other side, pulled it open, and walked in to find…

“What on Earth is going on in here…?”

Like the rest of the building, the room was filled with posters and figurines, but in here the theme was a bit different. Two words: hot guys. It was the polar opposite of everything I’d seen on display thus far. Maybe this particular room was meant to cater to the female demographic?

Regardless, I sat down at the table and wiped my hands with the hot towel the server gave me. Sitting on the tatami made me feel at ease, and contrary to my biggest fears, the menu was surprisingly normal. So I picked stuff at random, and when our boozy drinks arrived, I raised my glass for a toast.

“Well, uhhh… Here’s to being on the same team. Cheers.”

“Cheers.”

My throat was dry from nervousness, so I downed half my beer in a single sitting. Takigawa-san took a small sip of her light cocktail and set it on the table.

“Do you drink a lot?” I asked.

“I wouldn’t say a lot. I like it, but my tolerance is fairly low.”

“Gotcha.”

The conversation petered out. I’d done well to initiate some small talk, but I didn’t know how to keep it going. I just wished she would give me something to build upon.

For a while, the two of us drank in silence. Granted, mine was just beer, so I emptied my glass rather quickly while Takigawa-san was only one-third of the way through hers. Now I didn’t have anything to keep my hands occupied.

Then, around the time her glass was half-empty, she suddenly plunked it down on the table. “Hey.”

“Wh-what?!” I blurted back, startled. Pretty pathetic for a nearly thirty-year-old grown man.

She lowered her head, narrowed her eyes, and glared at me. Upon closer inspection, I realized her ears were bright red. Surely she couldn’t be drunk already…could she?

“Remember when we spoke in the research room on my first day?”

“Yeah?” My dad was the one who brought her in, as I recalled.

“You said ‘nice to meet you.’”

Indeed I had. It was the standard greeting—why change a classic? But that was when I remembered the suspicion I had that day…

“That was not your first time meeting me.”

Called it.

“Or at the very least, it wasn’t my first time meetingyou,” she clarified.

“Right. I suspected as much.”

“You suspected it? So you realized?”

“I just, uh…felt like I must have seen you somewhere before,” I stammered.

“Do you know where it was?”

“…Sorry, I can’t remember,” I admitted honestly. No amount of thinking had brought me any closer to the answer.

She took another sip of her drink. Was that why she seemed to be in a bad mood? Well, why couldn’t I remember her? Where the hell had the two of us met before?

“We were classmates. In high school.”

“Wait, what?”

“We were in the same grade, in the same class, at the same high school,” she said.

“…Oh god. I’m so sorry.”

So that’s where we’d met. No wonder I recognized her! Yes, it all made sense now—Psych! In truth, it still didn’t click for me whatsoever.

The high school I attended was the prefecture’s most competitive school, where students were sorted into classes based on their entrance exam scores. As the highest scoring student, I naturally ended up in Class A, the top class. But everyone in that class was only interested in studying, myself included, so there was basically zero socializing. I honestly couldn’t recall a single name or face from that time. How had I managed to recognize Takigawa-san?

“We never spoke back then, so I can’t blame you if you don’t remember me. But I imagine quite a few people remember you. After all, you were the first-year representative.”

Right. After earning the top score on the entrance exam, I was asked to give a speech as the valedictorian representing my entire grade, so I could understand how the academically competitive students in Class A might still remember me. But that still didn’t explain how I remembered her.

“I was hoping to get the highest score myself, so I was quite bitter. After that, I kept trying to outscore you on every test, but you got first place on every single one.”

That was back when Shiori’s body was still alive—back when saving her was still within my reach. I wanted to get perfect grades so I could get into the best possible college and find a way to rescue her. I studied my ass off to make it happen.

“You can imagine my shock when you dropped out in our second year,” she continued. “I’m sure there were extenuating circumstances, but at the time, I assumed you simply burned out. But oh, how wrong I was! After you dropped out, your causality radius theory was proven, and your name was added to the annals of imaginary science. When I first heard the news while in college, I was so deeply jealous. I swore to myself I would land a job with the Imaginary Science Research Institute and make a discovery that would eclipse yours.”

It had to be the alcohol. She was normally so calm and collected, but now her eyes pierced into me with passionate fury. Dad was right—I could certainly put this ambition to good use.

“I’m honored. May the two of us take imaginary science to even greater heights,” I said, offering a toast.

I donned my best fake smile, but on the inside, I still felt uneasy. Damn it, where the hell did I remember her from? It’d be one thing if I just recognized her name, but something was telling me there was another, vastly different memory. We may have been in the same class, but we never said a word to each other. After I dropped out, I didn’t see her again until that fateful day in the research room. So where could it have been?

She must have sensed the insincerity in my smile, because her expression soured again. She took a big gulp of her drink—the largest thus far. Whoa, is she okay there?

“And another thing.”

“Yes?”

“In order to have a fair competition with you, I have a request.”

“What is it?”

What was she about to ask of me? Hopefully, it was nothing that would take effort. She took another swig, then leaned across the table and said, “Can we cut the bullshit?”

“…Excuse me?” I didn’t know how to interpret that.

“Look, we’re the same age. We can’t talk like diplomats all the time or it’ll feel like we’re still at work. Besides, I can’t compete with you if I have to treat you like my boss.”

“Okay…?”

“So, how about it? Can we just be direct with each other? If you’d rather not, say the word and I’ll drop it. I do understand the concept of office politics, after all. You can just write this off as a drunken outburst.”

Did she get tipsy on purpose to find the courage to ask me that? Cute. But now that I thought about it, perhaps it was actually a good idea. I didn’t like walking on eggshells around colleagues, and besides, I might want to talk to her about my time travel research someday. If so, it couldn’t hurt to establish a casual working relationship early on.

“Okay, sure. Let’s both just drop the formalities. It’s easier that way,” I agreed.

“Cool, thanks,” she replied curtly, then downed the last dregs in her glass.

While she seemed calm at first glance, her hands were shaking faintly. She must have been scared stiff. After all, normally it’d be downright unthinkable to ask your boss to “cut the bullshit.” Luckily for her, however, I was no normal boss.

“Anyway, I look forward to competing with you, Hidaka-san.”

“Hey, if we’re dropping formalities, then you should just call me Koyomi.”

“Are you sure? All right then…Koyomi.”

And the instant she said my name, I remembered exactly when and where I had seen her.

***

As I recalled, it was back when I was about twenty years old. After dozens of parallel shift experiments, I had finally gotten permission for a long-distance shift. And so, for my next trip in the IP capsule, I decided I would go much, much farther than usual.

Our experiments were always conducted around 2 a.m., since it was too risky to shift during the day. If I shifted to a world where I was in the middle of traffic, the split-second mind lag could cause a major accident. That happened to Shiori, after all.

At 2 a.m., however, I was generally asleep. There was never a guarantee, of course, but more than 90 percent of the time I’d find myself lying in bed, just as expected. And this particular shift was no different in that regard.

But this time, there was a critical difference…and when I realized what it was, I very nearly screamed.

My right hand was clutching someone else’s.

Slowly, fearfully, I turned my head to the right.

Someone was lying next to me. I felt their skin and realized we were both naked. Through the dim glow of the nightlight, I could faintly see their figure. Long hair… A girl.

For a moment, my hopes soared. Could it be…Shiori? Could this be a world where she didn’t turn into a ghost after meeting me? The very world I’d sought all this time?

To find out, I fumbled for the lamp on the bedside table and switched it on. The sudden light woke her.

“Mmm…? What’s wrong, Koyomi?” Rubbing her eyes, the woman looked at me.

…Who the hell are you?!

“Need the restroom? Or…did you want to go another round?” she asked, smiling bashfully.

Her eyes, her ears, her nose, her smile, her voice—this wasn’t Shiori at all. It was someone completely different.

I was sleeping naked with some other woman?

The thought made me viscerally ill. I wanted to puke. I wanted to shove this woman away and angrily demand to know who she was.

Stay calm. Deep breaths. This isn’t my world, and I can’t dictate who my parallel selves can and can’t date…can I…? Hold on a minute. I mean, it’s still me I’m talking about. What the hell am I doing, sleeping with a girl who isn’t Shiori? Me, of all people! Doesn’t every me live solely for Shiori?!

I couldn’t think straight. I was too confused. I needed to just go back. Back to my world. And so, for the first time in years, I prayed. Hard.

Take me back. I can’t stay here. I’m serious. I refuse to accept that I could be with someone other than Shiori—!

And when I returned to my home world, I erased the incident from my memory.

***

Yes, it was in a parallel world. In that world, there was a woman who called me Koyomi. She was in bed next to me, holding my hand, smiling at me… She was my lover. But I couldn’t accept a reality where I loved someone other than Shiori, so I went straight back to my world.

I doubt anyone in that world even realized what had happened, since the trip only lasted a minute or so, and the other me was asleep at the time. But there could be no mistake: when Takigawa-san called my name just now, it sounded identical to the voice I heard in that parallel world. That was where I first met her—in bed, in an alternate universe.

Unsure how to process this revelation, I fell silent, and as if in my place, Takigawa-san spoke up. “Likewise, you can call me Kazune.”

If I wanted her to call me by my first name, then it’d be weird not to return the favor, so I forced my weirdly dry mouth to cooperate. “Sure thing…Kazune.” Though it was my first time saying it aloud, the name felt right at home on my tongue. Now I really missed Shiori.

After that, Takigawa-san…er, Kazune and I ordered a few more drinks while we ate dinner. By the time we left the restaurant, she was plastered. She begged to go to karaoke, so I humored her for an hour or so, then decided to walk her home to make sure she didn’t fall face-first into any bushes.

On the way, we arrived at the Showa-dori intersection. The light changed, and we began to cross the street. At the other end was the spot where Shiori was stuck; I focused my mind, and she floated into view, the spitting image of her fourteen-year-old self.

“Oh, hi, Koyomi-kun!”

She beamed at me, and I waved slightly. Unfortunately, I was with Kazune at the moment. No matter how drunk she was, I couldn’t talk to an invisible ghost in front of her; I didn’t want her thinking I was weird. And of course, I couldn’t exactly ditch her in her current condition. With no other option, I decided I’d come back to the intersection after I took her home.

I hung back for a second and whispered, “Sit tight for a bit. I’ll be right back.”

Shiori nodded slightly…and then…

“Wait, you can see that too?” Kazune asked.

I stopped dead in my tracks and looked at her. Sure enough, she seemed to be looking at Shiori. Neither my dad nor the director was able to see her, but supposedly there was a small percentage of people who could. That was how the urban legend about the “crosswalk ghost” got started in the first place. And if Shiori counted as a ghost, then perhaps those few had a particularly strong sixth sense. Was Kazune one of them?

“You’re telling me you can see Shiori?!” I blurted out, flustered.

Her unfocused eyes sharpened until they were piercing me with their usual force. She had switched back to researcher mode.

“Shiori? That’s the ghost’s name? Do you know this ghost?”

What a careless mistake. I tried to think of how I could talk my way out of it, but there weren’t any good options. And my awkward silence was already as good as a yes.

“I…I asked her myself,” I forced out as a half-hearted excuse, but Kazune’s expression was too vague for me to tell whether or not she believed me.

“It’s a she?”

“Yeah, isn’t that obvious?”

“So you can see her clearly enough to approximate her gender?” she asked.

“What?”

“I can only see the fuzzy outline of a person on rare occasions,” Kazune explained. “I certainly can’t hear her voice. But you can both see her and speak to her? There has to be a connection. Don’t even try to tell me otherwise.”

Now I’d dug my own grave even deeper. Did she set me up? She’d have to be quite talented to pull off a stunt like that while under the influence.

“Start talking, mister. I advise you not to underestimate my curiosity,” she said with an unwavering glare.

I knew any excuse I tried to make would be ignored. Worst-case scenario, she might let something slip at the lab, in front of the other researchers. So what was my move? This was a serious decision.

Kazune was an extremely gifted colleague. From the beginning, I had considered telling her about my real research in order to gain her assistance… Maybe the time had simply come a little earlier than I expected. Could this be my chance?

I looked at Shiori, who looked from me to Kazune with eyes as wide as saucers.

“Shiori, is it okay if I…tell her?”

She gazed back at me for a few seconds, then nodded her head.

Summoning my resolve, I turned back to Kazune. Another factor in my decision was that if I brought her into the fold, I might be able to talk to Shiori more easily. After all, I looked like a psycho talking to “myself” on the street corner, but with a second person standing there, people would assume I was talking to her. It wasn’t like anyone would stop and eavesdrop.

“Okay, Kazune. This is important, so I need you to listen carefully.”

And so I told her about Shiori. Not everything, obviously. I left out most of the messy details and said the two of us were just friends. But I gave her the general gist of it all: my friend got hit by a car in a parallel world, tried to shift away, but her physical body died before it could complete, and as a result, her imaginary elements were left stuck in that spot—AKA imaginary karyomitosis.

“And I’ve been searching for a way to save her ever since.”

Once I finished, Kazune pressed a finger to her lip in contemplation. Whatever she was about to say, for better or for worse, it would likely change my opinion of her forever.

“Well…perhaps we could, if we were able to observe imaginary elements with enough accuracy to pinpoint hers. Then, if we fused them back into her body…”

This answer scored very highly with me.

“Sadly, her body’s already passed away in this world. Imaginary karyomitosis manifests as brain death, and she only held out for a few years on life support.”

“I see…” she said, thinking. “What are our options, then?”

I had one final moment of hesitation, but ultimately decided to tell her. After all, she had listened to my whole story, and instead of asking questions, arguing, or even shrugging her shoulders, her first instinct was to start brainstorming a solution. She was a researcher through and through, and I wanted to trust her.

“I believe the only option is to erase the event that put her in that condition to begin with,” I said. “I just need to find a way to do that.”

“Erase the event?”

“The event that led to the accident. The event that caused her to shift in the first place. If we could undo it…”

“Undo it? Are you saying what I think you’re saying?”

She must have put two and two together. No surprise there. Anyone well-versed in imaginary science would have had this thought at least once.

“Yeah. This whole time, I’ve been researching time travel.”

Her almond-shaped eyes widened behind her glasses as she stared back in shock. In a time where something as improbable as parallel worlds had been scientifically proven, time travel still seemed like the stuff of fiction. Anyone would be baffled to hear that I was pursuing it for real.

“I want to go back in time and fix it. That’s my goal,” I said simply.

Spoken to the wrong person, a statement like that would make me sound insane. But Kazune was different.

“That’s incredible.”

“What?”

“You’re truly an incredible person, Koyomi. You’re not just researching parallel worlds—you’ve taken the next step.” Her eyes sparkled with curiosity toward the unknown. “I mean, there’s no way you’d get funding for that!”

“I know. I have to use the funding from my parallel world research instead, and if anyone finds out, I’ll lose more than just my job.”

“Secret research, hmm? Spicy. Consider me your partner in crime. Rest assured, I’llbe the first to find the key to time travel.”

“…You know, I always thought I might end up counting on you, but I never thought it’d be today.”

At this point, I knew we were stuck together for the long haul, but I had a feeling her competitive streak would work in my favor. As a researcher, the drive to be a pioneer was more important than you might think. I could only imagine how many things in life only came into being as the direct result of a friendly rivalry somewhere down the line.

“Modern imaginary science believes time travel to be impossible… That’s because vertical migration of physical matter has to break through the barrier of imaginary elements… Wait, but that’s only an issue in the model. If we were to design a new model… Gah, what am I doing just standing here? Koyomi, I’m going home!”

“Are you sure that’s a good idea? Aren’t you still drunk?”

“Nope. This conversation sobered me right up.”

“Want me to walk you there?” I asked.

“No, I’ll just hail a taxi. Need to get home ASAP so I can get all my ideas on paper. I’ll see you tomorrow!”

Without waiting for an answer, she started walking so briskly, you’d never believe she was staggering around just a few minutes ago. But after just a few steps, she stopped and looked back at me.

“Oh, and…Shiori-san, was it? Say hi for me.”

With that, she turned and walked away for real this time. As I stood there, I heard Shiori’s faint voice echo in my ears.

“She seems cool.”

“Yeah.”

“Is she your girlfriend?”

I glared at her on reflex. “No!”

“…Don’t glare at me…”

“Sorry. Anyway, no, she’s not my girlfriend. You’re the only one for me.”

At this, Shiori smiled—so weakly, I couldn’t tell if she was happy or sad. “Thank you, but… You can let go now, Koyomi-kun.”

That was the last thing I wanted to hear.

“I can’t tell how much time has passed, but…I’m guessing a lot, right? I mean, you’re all grown up now…”

Shiori’s appearance hadn’t changed a fraction since the day of the accident at age fourteen. Her mental age seemed older, but I couldn’t say she had matured, exactly. If anything, her thoughts and emotions seemed to be fading with the passage of time.

Her face just wasn’t as expressive as it used to be. Sometimes she smiled faintly, but she never cried or got angry anymore. Maybe that was to be expected, though. After all, she’d stood at this intersection alone for more than a decade now. An experience like that would erode anyone’s humanity.

“It’s okay to move on, Koyomi-kun. You shouldn’t live your whole life alone, just for me… I don’t want that…”

“I’m not. I’m choosing you because I want to.”

“And I appreciate that…but…”

“No buts! I promised you I would help you, no matter what. It’s my life’s purpose.”

“…Okay.”

Saying it out loud made my love for her swell in my chest, pushing me nearly to tears. I wanted to hold her in my arms, but she didn’t have a physical form. I couldn’t even hold her hand. It was so bitterly infuriating that it broke my heart into pieces.

“I’m begging you, don’t tell me to let go. I want to live for you and you alone. I promise I’ll find a way to save you, so just have faith in me.”

“Okay… Thanks, Koyomi-kun.”

She reached a ghostly hand in my direction, so I laid mine on hers. There was no physical contact, of course, but…I wanted to believe the warmth I felt in her palm was no mere figment of my imagination.

***

Starting the next day, with the acquisition of a talented rival-turned-accomplice in Kazune, I pursued time travel research with renewed vigor. The two of us brainstormed not just in the research room, but at the park, at the cafe, at karaoke, at each other’s houses, sometimes even at Otakitchen. This passion led to achievements in our regular research too, and the two of us rapidly rose through the ranks. As a result, we gained access to tools that were previously off-limits, and our research progressed even further.

Meanwhile, I visited the intersection every day to talk to Shiori. Sometimes Kazune would tag along and “talk” to her through me. I lived a fulfilling life both in and out of the lab. But in the end, with no leads for time travel and poor Shiori eternally trapped at the crosswalk, another full decade passed.

***

“Here’s your beer.”

Once the bartender set my glass down on the counter, I picked it up and drank it one slow sip at a time. Before I knew it, I was pushing forty, too old to chug drinks anymore. Gazing at the little anime figurine in front of me, I found myself admiring its craftsmanship.

This bar was located on the second floor of Otakitchen, the restaurant the director had recommended to me ten years back, and as with the first floor, every inch was covered in anime posters and figurines. After Kazune and I became regulars at Otakitchen, we started coming up here too. Same bartender and chef for the past ten years straight.

“Rough day, Hidaka-san?”

“My research is going nowhere these days, and I’m starting to burn out.”

Over the past ten years, imaginary science had progressed by leaps and bounds. The director’s IP capsules had been implemented around the world, enabling the exchange of information between parallel worlds through optional shifts. As a result, the multiverse essentially turned into a giant quantum computer, which led to the ability to observe imaginary elements directly, and that in turn led to even more breakthroughs.

The first discovery Kazune and I made together was the answer to why I was the only one who could see and hear Shiori.

Observing imaginary elements directly enabled us to measure Shiori’s IP without a physical body. Then, when we compared her IP with mine, we found that one segment was a perfect match. This suggested that our IPs must have synced up somehow when we climbed into the IP capsule and parallel shifted together. That was how I, and only I, could see and hear her. The thought of us carrying a part of each other warmed my heart.

Incidentally, the process of researching eventually made it impossible to keep the nature of my relationship with Shiori a secret any longer, so with her blessing, I told Kazune the full truth. She reacted pretty calmly, as if she suspected as much already.

IP bands had become a household item as well. The law required doctors to take IP measurements for newborn babies and get them fitted for an IP band with World Zero pre-registered. The whole world now accepted alternate universes as fact.

My father’s research into IP stabilization was complete as well. By monitoring the target’s imaginary elements at all times, they could be “locked” to prevent parallel shifts. This was mostly used to prevent unexpected shifts during important events like weddings, and also to prevent criminals from fleeing to other worlds.

And so, imaginary science had become an inescapable part of everyday life. Recognizing its value, the Japanese government established several new laws as well as a Ministry of Imaginary Technology. As a result, our laboratory was reclassified as a National Research and Development Agency and renamed the Japan National Imaginary Science Research Institute. My mother and father were still director and vice-director, respectively, but they were retiring soon. It wouldn’t stop them from carrying on with their research, but they both seemed ready to pass on the torch. At the rate things were going, Kazune and I were the most likely candidates.

Amid the glorious forward charge of imaginary science, however, I still hadn’t found a method of time travel. It felt like I had overlooked something—something critical, yet most likely extremely simple. But common sense always got in the way of imagination, so if I had to guess, Kazune and I had yet to truly think outside the box.

So, what was the answer? I just didn’t know. Frustrated, I downed my beer.

“Slow your roll, pal. You’re no young pup anymore,” the bartender smirked wryly as he took my empty glass.

I was getting tired of my usual beer, so I flipped open the menu and debated ordering something different for a change. As I scanned down the list, however, I spotted an uncommon option.

“You guys carry Guinness here?” A dark, near-black Irish dry stout. Supposedly people in Ireland drank it basically every day.

“Ah, yes, we started stocking it at a customer’s request. Ever had it?”

“A few times when I was younger. Maybe I should have it again for old times’ sake.”

“Sure thing.” He set an empty glass on the counter.

“Where is it?”

“I’m about to pour it. Check this out.”

Grinning, the bartender pulled the cork out of a bottle of Guinness and poured it in at full speed. The dark beer immediately turned to foam as it filled the glass. But then, something strange happened.

As the beer level began to rise from the bottom of the glass, I expected the bubbles to be pushed up along with it, and yet…they were sinking, rapidly. I stared blankly at the bizarre phenomenon. Something crazy was happening right in front of my eyes—I could feel it in my gut.

“What am I looking at?”

“Isn’t it cool? It’s called a Guinness Cascade. I don’t know how it works though.”

Thinking logically, it was pretty simple. Due to the viscosity of the beer, when the bubbles rose, the liquid within close proximity was pushed up along with them. But because its density was greater than that of the bubbles, that liquid was then pushed out to the edges, and a vortex was created within the widest part of the glass as the beer subsequently pushed the bubbles back down. And so, the bubbles “cascaded” with the beer along the edges—then rose back up at the center of the glass, where you couldn’t see it.

They don’t just look like they’re sinking… Some of them really are sinking!

“Viscosity of the beer… Bubbles… Imaginary elements… Yes, something like imaginary viscosity… Buoyancy of bubbles… Imaginary density… Sea and Bubbles of Imaginary Elements… Viscosity and buoyancy… Measure IP… Overwrite… Lock…”

The bartender called my name. “Hidaka-san? What’s wrong?”

At last, I had found it. This was what Kazune and I had overlooked by thinking inside the box.

Bubbles can sink!

***

I couldn’t wait another moment, so I paid my tab, dashed out of the bar, and immediately got in contact with Kazune. It was past 10 p.m., but luckily, she was still at the lab. Incidentally, both of us were still single at this point. I may not have had any prospects, but she certainly did, yet she chose to prioritize her work over all else. A scientist in her late thirties probably wouldn’t have an easy time finding a husband, so in a sense, perhaps she was even more of a workaholic than me.

In any case, right then, I was grateful for her presence. I grabbed a taxi to the lab, then brought Kazune into a private room.

“What is it? Is something the matter?” she asked, her expression dubious. I decided to cut right to the chase.

“I’ve found it. A method of time travel.”

Her eyes flew open. A little shock was understandable, of course. The thing we’d been chasing blindly for the past ten years was suddenly right in the palm of our hands. But she had known me for years now—well enough to know that when it came to Shiori, I’d never joke around.

“Explain.”

“Sorry—what I mean is that I’ve got a concept, that’s all.” And so, as I detangled my thoughts, I slowly began to explain my theory. “In the Sea of Einzwach, the world bubbles rise to the surface to represent the passage of time. So to go back in time, they just need to sink.”

“According to the model, yes, but we talked about that on day one. Bubbles can’t sink, so the only way to push them down is to exert some manner of force, but doing so risks popping the bubble entirely.”

“You’re wrong, Kazune. Bubbles can sink…under the right conditions.”

“Such as?”

“Viscosity. Ever heard of Guinness? It’s a viscous beer with very small bubbles. As long as the viscosity outweighs the buoyancy of the bubbles, we can create a downdraft with the resulting vortex that will push the bubbles down.”

“Again, we’re talking about a scientific model, right? It’s just a thought experiment. The hard part is actually achieving it in imaginary space.”

“We can. We just need to modify the IP capsule and IP lock.”

The instant I mentioned the very devices that were close at hand, her expression changed from disbelief to contemplation. That was my cue to explain the specifics.

“First, we expand the functions of the IP capsule to apply external pressure to the time travel subject to compress the associated imaginary elements. Next, we expand the functions of the IP lock to secure the newly compressed elements. Then we overwrite the IP in the surrounding imaginary space and create a small vortex to produce a downdraft. The shrunken elements won’t have enough buoyancy to combat the imaginary viscosity, so in theory they should start sinking!”

Slowly, silently, Kazune digested this information.

“In theory…yes, it sounds possible,” she said. “The problem is whether we can actually implement these expansions for the capsule and the lock.”

“That’s what we’ll research next. Now that we’re able to measure imaginary space directly, I’m sure we’ll find a way!”

“Oh, good grief. Another decade’s worth of work ahead of us…” She slumped her shoulders in defeat. Translation? She was on board. “And there are other problems too. Even supposing we do work everything out, how will we use it to save Shiori-san?”

It was a valid question. That was my ultimate goal, after all, and merely establishing a method of time travel wasn’t enough to achieve that. It all came down to how time travel could save Shiori. But, naturally, I already had a rough idea.

“During this process, bubbles that sink don’t float back up, unlike in the beer. They keep sinking backwards in time until the buoyancy and viscosity levels even out with each other. The key here is that we’ll need to have already found the IP of a world where Shiori will live happily ever after. Then we’ll carefully compress the bubble so it’ll sink all the way to that branching point. If it works, the post-branch bubble should stop and fuse with the pre-branch bubble. At this point, the bubble’s IP is overwritten. Then it reverts to its original size and buoyancy, and the fused bubble starts floating back up toward the future again. After that, I carry on with my life in the other world.”

Kazune listened to my plan with her eyes closed. Then, after a long silence, she opened her eyes and glared at me.

“Let me get this straight. You want to send your disembodied imaginary elements to a branching point in the past, fuse with it, and live your life all over again?”

“More or less.”

“And what happens to your body left behind here?”

“We’re subjecting it to the same conditions as imaginary karyomitosis, except the imaginary elements migrate vertically instead of laterally. If the physical matter is the body, then the imaginary matter is the soul. And without a soul, my body will be an empty husk… In short, brain death, I imagine,” I explained matter-of-factly.

At this, Kazune frowned. She didn’t look happy to hear it. “And who’s going to look after you?”

“Don’t know.”

“How will your mother and father feel after you’re gone?”

“Don’t care.”

Her frown deepened. Obviously, I could understand what she was getting at and how she felt; I wasn’t that heartless. But what else could I say? It honestly didn’t matter to me.

“This world did Shiori dirty, so I don’t care what happens to it. I’m taking her soul and leaving for a world where she’ll be happy. Nothing else matters.”

That was all I had left to live for. I had no use for a world where my Shiori would never be happy, so the two of us would leave. Everyone else could go ahead and enjoy the rest of their lives without us. There wasn’t a single shred of hesitation in my mind; I sincerely wanted this, from the very bottom of my heart. And unless Shiori could magically come back to life with her body intact, nothing could change my mind.

Kazune must have sensed this, because she let out a sigh.

“…For the record, this is a time paradox you’re talking about. If you disappear into the past, won’t every single event you caused disappear along with you?”

“The tenets of imaginary science suggest otherwise,” I countered. “Think of it like if I was a pencil: if it breaks after drawing a line, that doesn’t mean the line goes away.”

“One more thing. If you merge with your parallel self in an alternate universe, your imaginary elements will merge right along with you, so I doubt you’ll get to keep your memories or personality. You’ll lose all the knowledge you gained after the branching point, and you’ll have no choice but to trust your other self to do the right thing.”

“Fine by me. To me, the only real Shiori is the one I met in this world, and I’ll never forgive myself for destroying her life. I reject the event that ruined it all, and I reject the world for letting it happen. If our souls can have a second shot somewhere else, that’s all I need.”

“You’re actually insane, you know that?”

“Yeah, probably. If you don’t like it, you’re free to go. I’ll handle it myself.”

I meant it too. This was my personal research, and she had the right to opt out at any time. But her response betrayed my every expectation.

“Oh, I’m not going anywhere,” Kazune said. “God knows how many decades it’ll take without my help.”

Her expression had lost all edge, like a weight had been lifted from her shoulders. It was funny—I was expecting her to lecture me, or insult me, or maybe even punch me.

“Incidentally, there’s one more problem, isn’t there? If you use the IP capsule for time travel, then Shiori-san can’t go with you. She has no physical body, and her imaginary elements are stuck at the intersection. What’s the point of going by yourself?”

“Oh, right, that… No, I think it should be fine. I mean, our imaginary elements are partially fused together, remember? Any change to my IP ought to change hers too, so if I go back in time, I believe she’ll come with me. But of course, I’ll need to test it first.”

“I see. Sounds like a lot of hard work.”

Kazune shook her head in exasperation. She was acting so normal now that it was hard to believe she called me insane a minute ago. At this point I was getting suspicious, so I decided to ask her about it flat-out.

“So…you’re okay with this?”

“It doesn’t matter what I think. Your life, your choices,” she replied.

“Sure, but I’ve dragged you into it for years now.”

“And that’s my life, my choices. Besides…” She gazed wistfully into the distance and smiled. “I wish I knew what it was like to love someone that madly.”

Indeed, she didn’t seem to have anyone special in her life, not as far as I knew.

“By the way, what exactly qualifies as ‘a world where Shiori-san will live happily ever after’? Isn’t happiness subjective?”

“Yeah, of course. I’m not talking about a perfect world or anything. I just know what sort of world she’s generally the happiest in.”

And my life’s purpose was to take her there.

“Oh really? What sort of world is that?”

Fortunately, I had known the answer to that question for decades.

“A world where she and I never meet.”

Interlude

Interlude

KAZUNE SAID it would take ten years of work to arrange everything I needed to make time travel a reality. Sure enough, precisely ten years later, we finished the modifications on our equipment. From there, we performed dozens of experiments until I was confident that all would go exactly to plan.

There was just one problem left, however. Which world?

The Schwarzschild IP, or SIP, was the radius within which a given event was guaranteed to take place across all worlds. The SIP of Shiori meeting me was a perfect match with the SIP of Shiori suffering imaginary karyomitosis. In every world where we met, she would always die at the intersection and become a ghost. So the world I needed to merge with had to be a world where we never, ever met.

And so I began to shift through all the different worlds, searching for one where we never knew each other…but as I would soon realize, that wasn’t enough.

***

“We need a way to predict the future.”

That was the first thing I said after I got back from an optional shift.

Kazune furrowed her brow at me. “Excuse me?”

“Think it’s possible?”

“In theory, yes. Maybe if we input a world’s worth of data into a quantum computer or something.”

“Okay, you do that.”

“Are you out of your mind? You know I can’t!” she scoffed in exasperation as she helped me out of the IP capsule. “Where did this come from all of a sudden?”

“I’ve realized this method won’t work.”

“Why not? Surely there must be one world where the two of you haven’t met.”

Rest assured, there were plenty of those. However.

“Take the world I just visited, for instance. I can confirm that Shiori and I haven’t met in that one. I was working at the ISRI. But then…” The memory gave me pause, and I let out a sigh.

“Then what?” Kazune pressed when she noticed I’d stopped. I took a sip of tea to wet my whistle, then forced myself to continue.

“Someone’s wife and daughter walked in to bring a basket of snacks for the team. Apparently they hadn’t met me before, because they said ‘Nice to meet you,’ and…”

“…And? What about it?”

She didn’t seem to get it. I didn’t either, at first.

“I’m saying that even at our age, there’s always a chance we’ll meet someone new.”

At that, she paused for a moment…and then her eyes widened as she realized what I was saying. Finding a world where Shiori and I were guaranteed never to meet was singularly close to impossible.

For instance, at age fifty in my world, my parallel self would also be fifty. And there were infinite parallel worlds out there, with plenty of worlds where Shiori and I hadn’t met within those fifty years. One might think this meant I could take my pick of them. But no, that wasn’t good enough.

Suppose I chose one of those worlds where Shiori and I hadn’t met within fifty years, went back in time, and merged with it. What if we met the very next year after that? It was impossible to deny the possibility.

At this point, I couldn’t allow myself to meet Shiori at any age. The moment we met, it would ruin her life. That was the inalienable truth of my world.

“I see… So we need to predict the future,” Kazune muttered wearily.

Without a way to know the future, there was no telling which of these worlds would keep me and Shiori apart our whole lives.

“Well, what now? Do we give up?”

Of course, giving up was not an option. Not after how far we’d come.

“I’ll figure it out.”

And so I threw myself back into the IP capsule…in search of a method I wasn’t sure I could even find.

***

The parallel world I visited that day was one where I’d seemingly chosen to live with my mother after my parents’ divorce. Reminiscing, I stepped out into the backyard to find a small mound of raised earth off in one corner. Yuno’s grave.

After fifty years, I didn’t expect it to still be there. I pressed a hand to the earth and found it cold. I couldn’t remember Yuno’s warmth anymore.

Then I thought back to what Shiori had taught me. As long as Yuno was warm, you could play with her, pet her, talk to her—all kinds of possibilities. But when she died, she went cold. Without that warmth, her world and all its possibilities came to an end…

The next instant, a jolt of electricity shot through my entire body. I rushed back to my home world, and the instant Kazune opened the glass door, I started babbling without even waiting to get out of the capsule first.

“I got it! I worked out how to find a world where she and I never meet!”

Startled, Kazune patted me on the shoulder, urging me to calm down. Then she made me some tea. But even that wasn’t enough to quell my excitement.

“Listen to me, Kazune. I’ve got it all figured out this time!”

“Yes, yes, I’m all ears. What’s your solution?”

“First, we find a handful of candidate worlds. Then we monitor them over the course of a few years. Maybe decades.”

“Maybe decades? Why?”

To minimize the possibilities. To wait for the warmth of possibility to go cold. In short, I meant… “However long it takes for my life to start running out.”

She stared back in silent shock.

“Whether it’s a disease, an accident, or natural causes, we have to wait until I’m on my deathbed without having met Shiori. Any world that makes it that far gets my stamp of approval. If I travel backwards in that world’s time, then fuse with it, I’ll die without ever meeting her. And if, worst-case scenario, we somehow meet at the last second…well, I probably won’t ruin her life, right? Since I’ll be dying soon after.”

I rambled endlessly without even gauging Kazune’s reaction. Did my reasoning make sense? Was it coherent? Evidently, I had lost the rationality to decide these things for myself. Was my age creeping up on me, or was I a special breed of crazy? I wasn’t sure anymore.

“Well, what do you think?” I asked. “Could this—”

Only then did I finally look at her face and realize that she was looking at me with deep sympathy in her eyes. What? Why is she looking at me like that? Isn’t it the perfect plan?

“Look, Kazune, we’ve got another long road ahead of us, but…will you join me?”

She was the only person I could ask now, so if she said no, I was up a creek. Then she looked down at the floor and said, “It’s a little late to abandon you now, you dolt.”

***

After that, I went to countless parallel worlds and picked out my surveillance candidates. Now, I hadn’t planned for this, but these worlds all actually had one other thing in common. Be it as a friend, a girlfriend, a wife, a mistress, an arch-rival, or something else—in every single one of them, Kazune was a part of my life.

In this world, she had already helped me so much. In the beginning she was fiercely competitive, always trying to one-up me, and in the end, instead of finding someone else, she had chosen to entertain my madness right to the bitter end. In this world, she was a colleague, a rival, and pretty much the only person I could call a friend. That said, I didn’t know her real reasons for helping me. For as smart as I believed myself to be, she was the one thing I felt I’d never truly comprehend.

I really hadn’t done it on purpose, but…maybe I’d subconsciously picked all the worlds where Kazune was there for me. If so, I intended to take this information to my grave rather than let her find out.

After that, I spent the next twenty-plus years monitoring the candidate worlds. My sole emotional support was the smile I received when I visited Shiori at the crosswalk, her appearance still unchanged from the day she died. Over the decades, I went there every single day to talk to her. I didn’t care what time of day it was—and I’d long since stopped caring about what the passersby thought of me.

And so the death march through the desert continued…until at last, at age seventy-three, one of my parallel selves was diagnosed with cancer and informed that he only had six months to live. Six months was still a long time though, so I decided to wait a little longer.

Then July rolled around. By my calculations, my other self now had just one month left. In the event that his physical body died, the imaginary elements that gave form to it would be lost as well, and at that point I’d be unable to shift there. I didn’t know if the same applied to time travel, but considering I couldn’t test it beforehand, I had to assume I’d lose my chance.

That said, doctors weren’t always 100 percent accurate about life expectancy. My other self might live six extra months, or he might keel over tomorrow. Looking at it that way, I couldn’t risk him dying of cancer and throwing a wrench into my plans, so I decided it was now or never. Tomorrow, the day that marked one month left, I would go back in time to save Shiori. It would be my first and last experience with time travel, and I would never come back to this world again.

In the other world, where Shiori and I had never met, she had a happy family. As for me…I married Kazune and had a happy family of my own. Part of me couldn’t believe I would ever marry someone other than Shiori, but…eh, Kazune was a special exception.

With the date of my leap now in place, I looked back at my life thus far.

I had lived for so long. Too long. And for what? I had no wife, no children… What even was my life’s purpose? Because of me, the one person I ever loved was wiped from the face of the earth.

But, well, at least it was almost over.

Bubbles can sink.

At last, the time had come to do away with this world once and for all. Because to me, a world without her in it was as good as worthless.

Epilogue…or Prologue

Epilogue…or Prologue

FROM AN OUTSIDER’S PERSPECTIVE, maybe we looked like old friends—two septuagenarians sitting at the kitchen table, drinking tea together. And in a way, we were. But I was planning to erase this world, and the old granny across from me, Kazune, was my sole partner in crime.

“Can I count on you tomorrow?”

“…A bit sudden to ask that, isn’t it?” she said.

“We ran all those simulations to ensure we’d be ready at the drop of a hat.”

“Yes, I know. So you’re really going through with it, hmm?”

“We’ve been over this a thousand times. It’s my life’s purpose. Though I do regret that I’ll be dumping this mess on you,” I admitted.

“Oh, I don’t mind the mess. It’s too late to complain now, anyway.”

“No, no, there’s still time for you to back out. I’ll find someone else. I’m sure one of those young whippersnappers at the lab will jump at the chance.”

“Don’t you dare! We can’t subject our young talent to something this dangerous! If someone has to do it, it should be me. I don’t have many more years left in me, anyway.”

“Nah, you’re gonna live to a hundred. I can feel it.”

“Ugh, spare me.”

She took a sip of tea—cheap leaves brewed in a cheap pot. Fitting for a man like me, but I was sure she was used to the high-quality stuff. She was the only friend this old misanthrope could claim to have, and she drank my shitty tea. Bad taste, some might say. Maybe that was why she was willing to humor me and my crazy plan all these years.

“You know what? Forget it. If we’re doing this, then let’s do it right. Do you have the roster for tomorrow?” she asked.

“Here.”

“I see… The IP capsule will be available all day.”

“Yeah, I managed to finesse that. I made sure the security system can be disabled from the outside too. No one suspects a thing. Guess that’s a perk of being the boss, huh?”

Kazune and I had long since been retired by this point, but as the former director and vice-director, we were allowed to walk around the lab as we saw fit. We’d passed the torch to our most competent successors, of course, but there was still some knowledge only the two of us had. We frequently dropped by for experiments as though we fancied ourselves visiting researchers—all to lay the groundwork for our ultimate objective.

“So, do I just follow the plan as normal?” Kazune asked.

“Yeah, no changes.”

“Remind me again what’s going to happen to you?”

“We haven’t done any clinical trials, so I can’t say for sure, but I’ll probably end up brain-dead. Already prepared my will and testament and donor card, so there’s nothing to worry about,” I told her matter-of-factly.

She looked back at me sadly. Deep down, she was a truly tender-hearted woman…

“No one’s going to want your nasty seventy-year-old organs.”

…which is exactly why she kept her tone harsh: to prevent me from feeling guilty.

Unfortunately, I did feel a little guilty about what I’d tasked her with, but it was a matter of priorities. I wanted to save Shiori’s soul, no matter who I inconvenienced along the way. At this point, it was my life’s sole purpose.

Kazune and I had taken our time making the final checks. Failure was unacceptable, or more accurately, failure was too risky. We tried experimenting on animals, but it was hard to judge whether they succeeded, and obviously we couldn’t experiment on humans. Tomorrow would be our first and last human experiment. Theoretically speaking, it was guaranteed to go wrong somewhere—but hey, theories weren’t always right.

Once we finished going over the plan, Kazune took a sip of lukewarm tea and let out a small sigh. “You’re really going to turn me into a murderer?”

“No! As I’ve explained a dozen times now, it’s not—”

“Yes, I know. Technically, it’s not murder. But the fact is, my actions will render your body brain-dead. It all comes down to my perception of that.”

“If you don’t want to do it, I can always—”

“I said I’m doing it, damn you! Don’t make me repeat myself.”

“…Sorry.”

“If you were actually sorry, you wouldn’t do it in the first place, but…oh, whatever. Also, my tea’s going cold.”

At her prompting, I refilled her cup. I was asking a lot of her, so I was more than happy to heed small requests like these. But even still…as I watched her sip what had to be scalding hot tea, I decided to finally ask the one question I’d kept to myself.

“Why have you stuck around all these years?”

She set her cup down and exhaled heavily. “Intellectual curiosity, I’m afraid. I’ve never beaten you once, remember? You were even the first to figure out time travel. And as a scientist, I’d kill to find out if these damn bubbles really sink.”

“…I see.”

She most likely wasn’t lying, but I felt like she was omitting some part of the truth. Normally she looked directly into my eyes, but right now, she kept her gaze carefully averted. That said, I didn’t mind. It was my selfishness that brought her into this, and she was allowed to have a little selfishness of her own.

“It’s been a long time coming, hasn’t it?” she mused.

“Tell me about it.”

“Be honest—did you ever come close to giving up?”

“No. Because I knew the moment I gave up, my life was over.”

“I see… Yes, of course. You’ve always been like this. I swear I’ll never understand it,” she muttered wistfully.

Frankly, the feeling was mutual. To this day, I could never figure out how to categorize our relationship. “What I don’t understand is why you never got married.”

“Oh, mind your business. It’s not like you got married.”

“Mm… True.”

She had a point. For one thing, it wasn’t relevant, and for another, we were in the same boat. If I had to guess, she was probably every bit as kooky as I was.

“…All right, I’m leaving for the day. If you need anything, get in touch.”

“Got it. I’m leaving too, so I’ll walk you out.”

Together, we packed up and left the house. The one thing I was grateful to this world for was the fact that we had both lived in relatively good health all this time, with no major illnesses or injuries. We walked to the train station with no need for a cane, and when we arrived, I bid her farewell. “I’m headed this way.”

“I see. Where are you going?”

I suspected she already knew, but I answered nonetheless.

“Gotta go rescue the crosswalk ghost.”

***

The Showa-dori intersection was our city’s largest, splitting into four quarters almost exactly at the center. Styled as a pedestrian scramble, it naturally got a lot of traffic. In the past there used to be a big pedestrian overpass connecting each of the four corners, but people complained about the pillars impeding visibility for drivers, so the whole thing was torn down. The old photographs made it look so cool though! Whenever I came to the intersection, I’d often stop and imagine what it would have been like to walk across it.

On the southwest corner of the intersection, there was a patch of greenery too small to be called a park. There stood the Leotard Girl, a bronze statue of a curvy young woman shyly covering her chest with her arms. It had been there since before I was born, and I was used to seeing it, but I had no clue who the model was or why it was erected there.

More than fifty years had passed since the rumors of a crosswalk ghost first started. Walking north from the southwest corner, you might encounter the specter of a young girl with long dark hair. Some people claimed she was on her way to a rhythmic gymnastics competition when she was fatally struck by a car, so the Leotard Girl was erected in her memory. However, I knew that was nothing but fiction someone had cooked up. The ghost and the Leotard Girl had nothing to do with each other.

I stood at the intersection and checked the IP band on my left wrist. On the holographic screen, beneath “IEPP” was a six-digit numerical display with three integers and three decimals. The decimals were in constant flux, too rapid to follow with the human eye, but the integers held firm at 000. Sure enough, I was in World Zero. So I called out to the empty crosswalk.

“Hello there.”

In response, Shiori’s ghost materialized into view—a girl with youthful features and long, straight black hair cascading over her white dress. After all these years and everything I had done, she somehow still had the strength to smile at me when she saw me.

“Sorry it’s taken me so long,” I told her.

She cocked her head in confusion. Her every gesture was adorable.

Summoning all my love for her, I continued. “This is goodbye.”

At this, she frowned slightly, but I knew she wouldn’t be frowning for long. I was going to sink her bubble.

What a long, long life I had lived. It had all gone wrong the year I was ten, when I met someone I shouldn’t have. And four years later, she was hit by a car at this very crosswalk, and she turned into a ghost, all because of me.

Then sixty years went by—sixty damn years—and now, at last, I could save her.

“…What do you mean, goodbye…?”

She continued to frown as I explained to her what I was about to do. I was going to sink the Bubble of Einzwach all the way back in time to the branch that determined whether or not I would meet her, then merge with the reality where I didn’t. And because a portion of our imaginary elements were synced, she would be pulled back in time along with me. Together, we would run away to a new world and live happily ever after—at a safe distance.

Once I was finished, grief spread across Shiori’s face. “But I don’t WANT to never see you again!” she yelled.

“We don’t have a choice, Shiori. In every world where we’ve met, you always end up a crosswalk ghost. If I’m going to get you out of there, I can never meet you again.”

“No!”

“It’s okay. As long as we never know each other, you’ll live a happy life. You won’t have to be alone and invisible ever again.”

“No! I don’t want to be apart from you, Koyomi-kun!” She shook her head, her voice watery.

I could feel my heart breaking. “Shiori, please…I need you to understand…”

For the next few minutes, the two of us argued in circles. I need you to understand. No. We don’t have a choice. No. It’s the only way to save you. No, I want to be with you.

I mean, obviously I didn’t relish the thought of never seeing her again either, but at this rate, I would probably kick the bucket soon myself. And at that point, Shiori would truly be stuck here all alone at the intersection, unable to communicate with anyone, unable to age, possibly for all eternity. I couldn’t let that happen.

But…the more Shiori begged to be with me, the more my resolve started to crumble. I wanted to be with her too, damn it! That was what I wanted more than anything! But that would mean keeping her a ghost, and I could never make that choice!

Part of me wanted to save her. Another part of me wanted to be with her. I didn’t know which was right. So…I decided to gamble on a third option.

“You win, Shiori. Let’s promise each other something.”

“Promise what?”

“A month from now, on August 17th, in the new world…I’m going to come back to this intersection to get you. Meet me there.”

The first gamble was whether my parallel self would still be alive by then or not. By my calculations, August 17 was past the date he was expected to die.

The second gamble was whether we’d even remember we made this promise. Merging with our parallel past selves would most likely overwrite our personalities and memories.

And my third and final gamble was if, by some miracle, we were able to reunite in the other world, would it ruin her life all over again? Truth be told, this was already an inherent risk of my time travel plan. But if I could hold out until my final days, I hopefully wouldn’t have enough time to cause the same disaster all over again.

And so I caved at the very last second and left a loophole in my plan. If there existed some kind of higher power in this world, surely they would permit me one last moment of selfishness.

“August 17?”

“That’s right. August 17.”

Maybe she didn’t remember, but that was the date of the accident that turned her into a ghost. If I could meet her at this intersection on that date, perhaps I could save her for real this time.

“A month from today, in the other world. But we have to go back in time and start over from when we were seven, so it’ll be August 17, sixty-six years from then. As for the time…well, it’s 10 a.m. right now, so let’s go with that. I’ll show up at 10 a.m. to get you.”

“You promise?”

“Yes, I promise.”

She smiled wistfully, like she could see straight through to the future. “Sixty-six years… That’s such a long time…”

“Yeah, I know. But we’ve already known each other for nearly that long, see? If we can do it once, we can do it twice.”

The second go-around would be completely different, of course. She wouldn’t be in my life, and I wouldn’t be in hers. We would simply have to wait.

“Think you’ll remember?”

Nodding slowly, she smiled—so weakly, I worried she might fade away altogether. “I won’t forget. Ever.”

“…Okay, I gotta go now. But this goodbye won’t be forever. I’ll see you again, Shiori.”

“Okay. I’ll see you later.”

She waved goodbye with a smile, and I smiled back. Then I turned away from the crosswalk—away from her.

But just then…

“Koyomi-kun!” she called after me. “I’m really glad I met you.”

The words gouged my heart…and the ones that followed made me want to stop, turn around, run back, and hug her tight.

“Thank you for everything… I love you.”

***

The next day, once all our preparations were complete, Kazune and I arrived at the deserted laboratory and headed for the shift room with the IP capsule. Naturally, the door was locked, so we went to the storage room and pulled out the box with all the keys, but…

“What the…?”

“…It’s not here.”

No matter how hard we looked, the shift room key was nowhere to be found. The last person to use the room must have put the key in their lab coat pocket and accidentally walked out with it. That was a fairly common occurrence.

“Well, now what? We can’t enact our plan,” Kazune remarked, though I sensed she was more relieved than she let on. Even as the minutes ticked down, she likely still had some lingering regrets about going through with this.

I, on the other hand, had come prepared. “Never thought I’d actually need to use this damn thing,” I muttered as I pulled a single key from my pocket.

“What’s that?”

“Spare key for the shift room.”

It was the one the director had given me at age fourteen—the one Shiori had made in secret. Back then, I wanted to believe that this key would open the door to our happy life together… The timing now felt like destiny indeed.

“Well, all right then. In we go.”

Kazune didn’t protest further. Once she agreed to something, she was the type to commit to it, 100 percent.

Inside the shift room, we prepped the equipment. We had run countless simulations and all that remained was to go for it.

At this point in my life, I’d climbed into the IP capsule hundreds of times, but at my current age it posed a bit of a challenge. Kazune did her best to help me, of course, but she was no spring chicken herself. Once I got myself settled, she closed the glass door…but then I thought of something and called out to her.

“Hey Kazune, I want to do an optional shift first, just in case.”

“What? And go where?”

“Same world I’ll be merging with. Just wanna check it first.”

“Fine by me. Same IP, right?”

“Right. Pull me back after five minutes.”

“Will do. Ready?” She set it all up with a practiced hand, then started counting down before I could prepare myself. “Five, four, three, two, one… Shift: on!”

I closed my eyes. I could feel the magnetic field humming to life inside the capsule, ever so faintly warm. And the next instant—

My whole body was suddenly racked with pain.

I opened my eyes. This was my bedroom, one I’d visited dozens of times now. In this world, I spent the majority of the day in a geriatric bed. As for the pain, it was from the cancer. Though I’d experienced it a handful of times previously, it never got any easier.

Enduring the agony, I looked at my left wrist. Sure enough, I was wearing my IP band. I pulled up the schedule app and put in a calendar entry.

August 17th, 10 a.m. Showa-dori intersection, Leotard Girl.

My meetup with Shiori.

Was this cheating? Well, I was trading my entire life for one fleeting encounter. Surely I was allowed to give myself one little hint, right?

Once I made sure the entry was saved, I wondered what my other self would think of this mystery appointment he wouldn’t remember making. Maybe he’d think he was going senile. Well, it didn’t matter to me as long as he lived long enough to go there.

Five minutes later, when I returned to my home world, I found Kazune looking pointedly down at me through the glass.

“Honey, I’m home,” I joked.

“Welcome back,” she replied, running her hand over the glass. “I had a nice little chat with your parallel self.”

Now this was a surprise. I had shifted there several times before, and Kazune had helped me with nearly every one of them, but normally she strictly avoided getting too involved with my other self. Before now, she never opened the capsule door or even spoke to him. But this time, of all times, she had made an exception? Could she no longer suppress that unquenchable curiosity of hers?

“What did you talk about?”

“Oh, we mostly just said hi… He took one look at me and called me Kazune straight away. To think he’d recognize me through all the wrinkles!”

“Hm.”

“Even in that world, I can’t seem to get rid of you, can I?” she asked.

“Er… I guess not…”

The conversation petered out, and for a while she seemed to ponder something—what sort of relationship our parallel selves had, perhaps?

Her expression shifted. “You know, I’ve been keeping this question to myself, but…I mean, at this point, you don’t mind, do you?” she asked casually, like it was a weight off her shoulders. “Tell me, Koyomi, what sort of world did you choose?”

She may have known its IP, but I hadn’t told her a single detail about what my new world was actually like. Admittedly, she never asked, but clearly she was curious. Anyone would want to know what was so great about the other world that I was willing to abandon this one. I contemplated how much to tell her.

“…In this other world, I call myself Grandpa, in the third person.”

I know, she mouthed back at me.

And “Grandpa” had spent his life loving Kazune instead. But again, I decided not to tell her that.

“I have a wife and son, and I’m pretty sure you and Shiori have happy families too. We all do.”

“…I see.” Evidently, she didn’t have any further questions.

After that, our chitchat was over, and we went back to our prep work. It was the same procedure as all the other tests, just one last time. Our setup went smoothly, and we were done in about an hour. Once she powered on the IP capsule, it was all set.

The branching point was at age seven: the parent I chose to live with after their divorce. As long as I chose my mother, I’d never meet Shiori.

In just a few moments, my imaginary elements would sink through the Sea of Einzwach and vanish from this world, taking Shiori’s ghost along with me. All that would be left behind was my brain-dead body, and the rest was up to Kazune.

“Any last words?” she asked me through the glass.

Since this was my last chance, I decided to tell her my honest feelings. “Thank you for everything. I’m truly glad I met you, and I’m sorry for the mess.”

“Oh, it’s fine. Too late now.”

That was our final conversation. I didn’t say goodbye—not out loud, at least. My life was dedicated solely to Shiori. But if I had to give thanks to one other person, it would be Kazune without a doubt. In a sense, she was a closer friend than Shiori ever was.

The IP capsule hummed to life, and the countdown to time travel began.

“Ten, nine, eight, seven, six, five, four…”

Then, in place of the rest, Kazune looked down at me and spoke. “Farewell, Koyomi. I wish you all the happiness in the world.”

She sent me off with the very words I’d chosen to leave unsaid—and in all the decades I’d known her, her voice was softer and sweeter than I’d ever heard it.

***

As I sink into the imaginary sea, holding this piece of Shiori, I bid farewell and take the plunge into a world where I will never know her.

Thank you for everything, Kazune.

And to me—the one who loved you—I entrust one fateful meeting.

All so I might see my beloved one last time.

Interlude

Interlude

THE NEXT THING I KNEW, I was standing there—smack dab in the middle of the crosswalk at a big intersection.

Where was I? I could vaguely recognize this place, but not really.

The cars came rushing at me—but they went right through me. Then the signal changed, and the pedestrians started walking—but they went through me too.

Light and sound… People and air… It all blew past me like I wasn’t even there.

Like I was some kind of crosswalk ghost.

What was I doing there? How long had I been there? I had no clue. I wasn’t even sure who I was.

I could have sworn I was just with someone a second ago, but whoever they were, they must have left me behind.

Still…alone and confused though I was, for some strange reason, I felt no fear, no anxiety, no loneliness. I knew only one thing for certain.

I was waiting for someone.

Waiting…and waiting…and waiting…

Right here, at the crosswalk, for you.