Chapter 8: The Difference

In the end, I went to school together with Kameyama Number Three.
Which meant I wouldn’t be able to observe the exact moment when he did something different from usual.
And that had to be where the key to crossing world lines was hidden.
Granted, he was already doing something unusual right now...
But I seriously doubted talking to me was the secret to crossing world lines.
“Hamori-san, do you always come this way?”
“Um, yeah. I do.”
I had been stalking him every single day for a year, so yes, I came this way every day.
Technically, I wasn’t lying.
Although if you compared it with the actual route from my house to school, this was one hell of a detour.
“I see. I’m always cutting it close, so you probably pass through here before me.”
Nope.
I follow you.
Which is why I also end up barely making it to school every day.
If he would just acknowledge me as his girlfriend, I could come wake him up every morning like some childhood friend character from an old Showa or Heisei rom-com.
I was already coming all the way to his house every day anyway.
It wouldn’t be a burden at all.
If anything, I’d consider it a reward.
...
Was I actually kind of dangerous?
But he wasn’t the Kameyama-kun I loved anymore, so I probably wouldn’t go wake him up.
“I won’t tell anyone about yesterday, so don’t worry.”
“Please don’t.”
You know that girl? She was bawling her eyes out in the classroom yesterday.
Yeah.
No thanks.
Still, since he was at least very close to being Kameyama-kun, I trusted that he wouldn’t go around spreading it.
“Aren’t you going to ask why I was crying?”
“I think if you want to cry, then crying is enough of a reason.”
“...”
Kameyama-kun had been like that too.
I used to think that if my feelings weren’t something society would approve of, then I had to deny them.
That kiss had freed me from that way of thinking.
That was one of the things I had fallen for.
“...Maybe that’s why you’re so bad at comforting girls.”
“Yeah. Maybe. Sorry.”
“It’s fine.”
It actually wasn’t.
I wanted him to stop.
He really was too much like Kameyama-kun.
I didn’t want him showing me the parts that were similar.
Every time I talked to him, I wanted to see Kameyama-kun more.
The urge to throw my arms around him kept bubbling up inside me.
My romance was finally supposed to happen.
Instead, it had been put on hold.
And I was annoyed.
I had waited patiently for an entire year, only to get stood up and handed a four-character message saying Wait for me.
Last night, I had been overjoyed just knowing he still existed.
Now I wanted to yell, What the hell?
You took away the thing I’d been waiting a whole year for.
How was that fair?
But if Kameyama-kun had some reason for it—
if that Wait for me was the absolute most he could do—
then I had to move.
When I thought about it, it made no sense that an idiot willing to prioritize my wishes over the collapse of the world would simply fail to contact me.
Standing me up made even less sense.
So those four characters must have been everything he was capable of sending me.
I had no choice but to believe that.
I looked at Kameyama Number Three walking beside me.
When I thought I might never see Kameyama-kun again, I hadn’t even wanted this guy in my field of vision.
But things were different now.
He was my clue to finding Kameyama-kun.
So I had to observe him.
Talk to him.
Find some kind of hint.
When had he changed?
“Kameyama-kun, do you remember what you ate yesterday morning and at lunch?”
He looked confused for a second at the sudden question, but answered honestly.
“For breakfast, toast, a fried egg, and sausage. Lunch was... uh... the twice-cooked pork set from the cafeteria, I think.”
“I see.”
That matched my observations.
He really had eaten that yesterday.
The fried egg and sausage were his usual breakfast.
Lunch changed every day because the school used a contracted lunch service.
But he didn’t remember me giving him the novel.
That happened just after we switched to summer uniforms.
More than a week ago.
If Kameyama-kun had already changed more than a week ago...
then I had been stalking a different version of him without noticing.
Ahhh!
What kind of idiot was I?!
I had been stalking someone and failed to notice that the target had changed!
My entire record as a stalker was crumbling before my eyes.
Farewell, my one-year career.
Which raised another question.
Where had the Kameyama-kun who disappeared that day come from?
Yesterday, I saw him vanish right in front of me.
That Kameyama-kun had definitely been the one I wanted to see.
Wait.
This whole Kameyama-kun, Kameyama-kun thing was getting impossible to follow.
From now on, I’d call the Kameyama-kun I wanted to see by his first name.
Hiroki.
We weren’t dating, but I was calling him by his first name anyway.
The Kameyama-kun I didn’t know would be Kameyama-san.
There.
Much clearer.
Now, back to the investigation.
My beloved almost-boyfriend Hiroki had only appeared during that one instant on the day he vanished.
Which meant that at that moment, there may have been two people named Kameyama at school at the same time.
Hiroki and Kameyama-san.
Yesterday, I had been following Kameyama-san on the way home.
But tailing someone inside the school was actually pretty difficult.
There was a much higher chance other people would notice.
You had to pretend you were just using your phone, or waiting for someone, or doing something else while secretly following your target.
So there was no way I could keep my eyes on Kameyama-san every second.
If two people who looked exactly the same switched places, I probably wouldn’t notice.
Maybe that was how it worked.
Let’s organize this.
I gave Hiroki the novel more than a week ago.
At some point between then and yesterday, he was replaced by Kameyama-san.
Then yesterday after school, Hiroki came back for only a moment.
Think, me.
Hiroki went to that room where we kissed on a day when sixth period was PE.
The fact that he wasn’t wearing an undershirt made that obvious.
Yesterday was also a day when sixth period was PE.
But by that point, Hiroki had already been replaced by Kameyama-san.
PIROROROROOON!
Detective Hamori Momoka—
at that moment, lightning shot through my brain!
Hiroki had jumped from last week...
to yesterday, one week into the future.
From Hiroki’s perspective, he received my novel.
A few days later, he jumped one week ahead.
Then he came to the classroom, where I saw him.
And from there, he jumped into that room from one year ago.
Yes.
Yes!
Good.
I was starting to understand Hiroki’s movements.
And that meant I was starting to understand who Kameyama-san was too.
Kameyama-san was someone who had appeared to fill the one-week gap left behind when Hiroki jumped through time.
...
Hm?
No.
I still had no idea who he was.
What did “someone born to fill the gap” even mean?
That was terrifying.
“Kameyama-kun... are you secretly an android?”
“IT APPEARS MY TRUE IDENTITY HAS BEEN DISCOVERED.”
“W-Wait, seriously?!”
“Kidding. What the hell do you mean, android?”
“Ahaha. Right.”
So Kameyama-san was actually pretty good at playing along.
I hadn’t known that.
How much did I really know about Hiroki?
I had spent an entire year stalking him.
I knew which movies he saw at the theater.
Who his friends were.
Which leisure spots he visited.
But I didn’t know how he felt about those movies.
What he thought about his friends.
What went through his mind when he looked at the animals in an aquarium.
I didn’t know any of the things that actually mattered.
Even though I knew his phone bookmarks included things like wholesome older-woman stuff, lovey-dovey literary-girl stuff, and childhood-friend classmate stuff.
Even though I knew he used his birthday as the PIN to unlock his phone.
I knew all that.
And still didn’t know the important things.
I really did want to see him.
I wanted to talk about everything.

After we got to school, I spent the whole day observing Kameyama-san with my now well-honed technique—
during class, between classes, whenever I could.
And I figured out something important.
He was a human being.
That sounded incredibly obvious.
But that morning I had seriously wondered whether he might be an android, so it was actually a small but necessary discovery.
He had a personality.
A sense of self.
Friends.
A life.
If I wrote out his profile, there was basically no difference between him and Hiroki.
Same birthday.
Same favorite foods.
Same friends.
Same best subjects.
Same talent for drawing.
He was incredibly similar to Hiroki.
No.
“Similar” wasn’t quite right.
So much of him was exactly the same.
The way he laughed.
The habit of spinning his pen.
The way he walked.
The way he looked left more often than right.
The way he suppressed a yawn.
Even his handwriting and the way he took notes.
All the same.
The differences were simple.
He hadn’t read my novel.
And he hadn’t kissed me.
Not only did Kameyama-san not remember me giving him the novel, none of the friends who had been nearby remembered it either.
Some kind of effect had erased the fact that I had ever handed it over.
I couldn’t confirm in a single day whether Kameyama-san was also some spacetime-hopping agent.
But if he was this similar, he probably was.
I’d check later.
It was easiest to think of Hiroki and Kameyama-san as two different people who happened to be very similar.
Except...
they were too similar.
Even identical twins wouldn’t match this closely.
A thought suddenly occurred to me.
Wouldn’t it be easier just to settle for Kameyama-san?
Why not make Kameyama-san my boyfriend?
There were so many parts of him that were the same as Hiroki.
Actually, “the same” was probably more accurate than “similar.”
Of course, even if they looked identical, that didn’t guarantee their minds were identical.
But suppose they were.
What would that mean?
How would getting to know Kameyama-san be any different from getting to know Hiroki?
Same face.
Same body.
Same voice.
Same personality.
Same character.
Same past.
Anything I learned from him would probably be the same too.
So what exactly was different?
Could I really say that communicating with Kameyama-san was not the same as communicating with Hiroki?
No.
No, no, no.
They were different people.
Yes.
Kameyama-san and Hiroki were different people.
Communication wasn’t just about Hiroki telling me something.
What mattered was that both of us knew the exchange had happened.
If Kameyama-san told me something, Hiroki wouldn’t know about it.
It had nothing to do with him.
Learning information about Hiroki without Hiroki knowing...
wasn’t much different from stalking.
It wasn’t communication.
I thought about it from every angle.
But in the end, the decisive difference was still the first kiss.
Hiroki mattered because he was the person I shared that irreversible kiss with.
If I kissed Kameyama-san...
I probably wouldn’t feel this way.
...
Right?

After school that day, I went to the literature club room for the first time in a while.
On the right was a faded whiteboard worn dull from years of use.
A long table stood in the center.
At the back, dusty novels written by upperclassmen were packed onto the bookshelves.
The lower shelves held reference materials.
Books on screenwriting.
How to write novels.
Dictionaries.
Thesauruses.
And all kinds of sourcebooks useful for history, science fiction, and other settings.
There were only five members in the club now.
And only two of us had shown up today.
Me and Hayakawa Akemi.
When I opened the door, Akemi greeted me with a lazy, “Ooh.”
“Momo-chiii, it’s rare to see you here after school. You finally done stalking your beloved Kame-chii?”
She glanced at me, then lazily lowered her gaze back to the mystery novel in her hands.
“No. Looks like the stalking is going to continue.”
“Why not just talk to him normallyyy? Stalking someone for a whole year is weeeird.”
“Honestly, I want to stop too. I’m not doing it because I enjoy it anymore.”
“That’s obviously a lie. You totally enjoyed it before.”
“...I did before. But now I’m being forced into it by something much bigger than me.”
“I’ve never heard of mandatory stalking. Since when did Japan become a country that forces people to stalk each other?”
While we talked, I headed toward the back of the room.
My target was the bottom shelf.
The science-fiction reference books.
I pulled out an oddly thick volume and spread it open on the long table.
“Huh? Momo-chi, weren’t you all about history and romance? Since when are you interested in sci-fi?”
“Please. I need advice.”
I leaned across the table and practically grabbed Akemi’s hand.
The novel she was holding dropped to the floor.
“O-Okay...”
She agreed, slightly taken aback.
“Do you know how to cross world lines?”
“MOMO-CHI IS FINALLY MAKING HER SCI-FI DEBUT?!”
This time, she lunged straight into the conversation.
It made sense.
When someone close to you started writing in your favorite genre, it was exciting.
Though it also tended to make you way more opinionated and critical about their work.
“Yeah. That’s right. I’m writing sci-fi now. The setup is a romance where a girl wants to meet the boy who jumped beyond her world line.”
“Oooh. You thought this through.”
Akemi crossed her arms and nodded.
Less thought this through and more this is literally happening to me right now.
“In modern romance, the idea of family has weakened, and distance isn’t much of a barrier anymore, so basically the only thing that can truly separate two people is death. I always assumed that was why you wrote historical romance, Momo-chi. But with sci-fi, you can separate the lovers with different world lines...”
“Y-Yeah. Exactly.”
Everyone in this club started talking at double speed the second the subject turned to their favorite genre.
She was analyzing it all on her own, but I had never once thought about any of that.
There were plenty of obstacles to romance in modern stories besides death.
Love rivals.
Unstable psychos.
Mothers-in-law.
“When people explain concepts of time, they often talk about presentism and eternalism. Thanks to relativity, eternalism has become a lot more mainstream, so I’ll just explain that one.”
“Yes. Please do.”
I straightened my posture.
This was information I needed if I wanted to see Hiroki again.
Akemi flipped quickly through the reference book.
She had read it so many times she remembered exactly where everything was.
Impressive.
Then again, I was the same way with historical references.
“This diagram makes the concept of time pretty easy to visualize.”
“What is that?”
It was a strange picture of two cones joined together at their tips.
Almost like an hourglass.
At the narrow point in the center—the place where only a tiny stream of sand would pass—there was a thin plate.
“It looks like an hourglass.”
I said exactly what came to mind.
“Oh, yeah. It kind of does. This narrow point is the present. The top is the future. The farther up you go, the farther into the future. The bottom is the opposite—the past.”
Akemi traced along the outside of the cone with her finger.
“As time passes, the range of possible futures gradually spreads wider.”
“So the angle represents the range of possibilities?”
“Exactly. You’ve written time-slip stories before, Momo-chi, so you catch on fast.”
Right.
The whole thing where the future branches depending on your choices.
You saw it all the time in time-leap stories.
The protagonist made a different decision, and the story changed.
It felt like a very human-centered way to look at things.
Wouldn’t the future also branch if an insect or small animal made a different choice?
But there was no point overthinking that.
It didn’t really matter here.
“Does the range of possibilities spread into the past too?”
“Of course. You probably know more about that side than I do.”
“True.”
History changed all the time.
It used to be Create a Good Country, Kamakura Shogunate, 1192.
Now it was Create a Good Box, Kamakura Shogunate, 1185.
History wasn’t some perfectly fixed past.
The farther back you went, the more uncertain it became.
Maybe in that sense, it wasn’t so different from the future.
“So, what does it actually mean to cross world lines?”
Akemi drew two lines upward from the narrow point at the center of the hourglass-shaped diagram.
“To jump from this line to that line. That’s crossing world lines. I’m simplifying it a lot, but that’s basically the idea. The details are all in this book.”
“And does it say how to actually cross one?”
“That’s where the writer gets to show off.”
So crossing world lines really was something that belonged in fiction.
Not something reality had an actual method for.
“So it really is impossible...”
“Hey, don’t look so crushed.”
If there was no way for me to go to him...
then all I could do was wait.
Again.
I couldn’t stand that.
This time, I had no idea how many years I might have to wait.
“No. There’s still someone who might be able to help.”
Akemi suddenly gave me a new thread of hope.
“Who?”
“Kame-chii’s dad.”