Our parents had long since known about our relationship, so when we told them we were getting married, their only reaction was “Finally!” However, because both of our families were relatively wealthy, they nearly strong-armed us into having a big, lavish wedding. But neither of us were all that fond of the spotlight, so we desperately convinced them into letting us plan a small ceremony with family only. In exchange, we agreed to hold it on a traditionally auspicious day, lest we jinx anything.
From there, once we reserved a venue, all that remained was to wait six months until the big day. Around the time we were ironing out the small details, however, we encountered a problem—or should I say, re-encountered. One that all of humanity was forced to confront sooner or later, now that parallel worlds were an accepted part of life.
I first became strongly aware of this issue during my second year of college. Kazune had just turned twenty, and we decided to celebrate by drinking together for the first time. The party was held at my apartment, just the two of us.
“Happy birthday, Kazune.”
“Thank you.”
She blew out the candles adorning her mini birthday cake, and the room went dark. Then I got up, flipped the lights on, and opened a bottle of slightly pricey champagne. The pop of the cork and fizz of the bubbles felt like tiny fireworks in my ears.
Together, we ate some cake and each other’s home cooking, and then we had our official “first tastes” of alcohol. Both of us lived alone, and with our phones turned off, no one could interrupt our fun. We had yet to consummate the relationship, but she had agreed to spend the night, and we were getting tipsy… I’m not sure if I should say I was expecting it, but I was certainly intending for us to finally go all the way that night, and I suspected her intention was the same. She drank a tiny bit of alcohol, pretended to get really drunk, then let me guide her to bed, blushing all the way to her ears.
It was the first time for both of us, so we started by awkwardly linking our fingers together. Desperately willing myself to go slow, I peppered kisses across her cheek and neck before starting to take her clothes off.
And then, while I was kissing her left palm, I saw it. Her IP band displayed 001.
Kazune had parallel shifted. The girl I was kissing was the Kazune from the world next door. The instant I processed this, my mind went blank, completely wiping away the pleasant buzz of alcohol and arousal. That was the moment I first became aware of this issue.
There were limitless parallel worlds, and we subconsciously shifted across them on a daily basis. The farther the world, the harder it was to shift there; conversely, worlds within a range of three were nearly identical to our home world, so we’d often shift there and back without ever realizing.
At some point tonight, Kazune had shifted one world over. The closer the world, the smaller the difference, so I suspected our parallel selves had thrown the exact same birthday party we did. But…did that give me the right to have sex with this Kazune? Was this really still my girlfriend?
“What’s wrong?”
She noticed that I stopped and cupped my cheek. Wordlessly, I pointed to her IP band, and she gasped. Now she understood that she was in the world next door.
“What about yours?”
At her prompting, I showed her my IP band: 000. I hadn’t shifted.
“I see… Well, this certainly is a pickle,” she said.
Like me, she froze for a long moment. Then, with a sigh, she sat up in bed, having returned to her usual self. Frankly, I was in no mood to continue either. I sat beside her and heaved a sigh of my own.
“Should I assume these were very similar circumstances?”
“Probably. We were having drinks for my twentieth birthday, and one thing led to another. No clue when exactly I shifted… As far as I can tell, your room is identical to his.”
“Why did it have to be now, of all times…?” I complained.
“I’ll apologize if you’d like, but it’s not really my fault.”
“Yeah, I know. Eh, I’m sure there’ll be a next time… Back to the booze?”
“Yes, please,” she said.
We returned to the dining table and picked up where we left off drinking. I was warned the first time didn’t always work out, so I was somewhat prepared for that, but I never thought this would be why. Unable to truly escape sobriety, we fumbled our way through conversation until we arrived at our old standby: parallel worlds.
“To think that a mere ten years ago, parallel worlds were purely the stuff of fiction,” she said.
“They were researching it well before that, but that’s when it first went public, yeah.”
“Does that mean people in the past had experiences like these all the time, but simply never noticed? They made love to their parallel partners?”
“They must’ve. Without our IP bands, I wouldn’t have noticed either…” I said. “Man, if we took them off even a moment earlier, we might have kept going without a clue.”
“That’s a little frightening.”
“Yeah… But I mean, to be fair, our worlds are next-door neighbors. We’re more or less the same exact people.”
“You consider your parallel selves to be the same as you?” she asked.
“For the most part, sure… Oh, but if he was from World 100 or 200 or something, he might be some kind of serial killer. Wouldn’t want to associate myself with that guy.”
“But he’s from a parallel world, just like all the rest. Where do you draw the line?”
“Well…logically, there probably isn’t a line at all,” I reasoned.
“So no matter how different they are, they’re all still you?”
“Logically, yeah.”
“Then…why won’t you have sex with me?” she asked.
Why? The answer was simple. “Because I can’t think ‘logically’ when it comes to you. Back in your world, my Kazune is having the same conversation with your Koyomi. I bet they feel almost the exact same way, and they’re saying nearly the exact same things. But if I imagined your Koyomi making love to my Kazune? I’d go insane with jealousy.”
I didn’t want to even think about her sleeping with someone else, even if that “someone else” was a parallel version of me. And if I had sex with this Kazune, the same event would probably happen in the other world too. Because of that, I could progress no further.
“Ah. Yes, I can imagine that.” Frowning, she took a sip of her drink. She must have envisioned the same thing. Incidentally, because of her low alcohol tolerance, after just one glass of champagne, she had downgraded to a wine cooler with 3% ABV. “But I mean, we’ve seen so many films about parallel worlds…”
A rather sudden change of topic—or was it? Regardless, I nodded.
In the decade or so before we were born, parallel worlds were a popular theme in manga, books, movies, and TV shows. The woman who founded the real-life Imaginary Science Research Institute, Professor Satou, openly attributed much of her inspiration to those stories, and many of her discoveries and theories were named after them. We consumed a lot of that media ourselves in the name of research as well.
“In almost all of them, the protagonist tries over and over again to change the future into what they want, right? It makes me think—just because the protagonist doesn’t like what happens in a parallel world, does that make it bad? Even though it was constructed by their parallel self?” she asked me.
“Well, people depicted parallel worlds in a lot of different ways back then. But now that we know they’re real, those types of stories probably won’t get made anymore.”
“Right. I mean, time travel isn’t even possible. If you really wanted to undo a mistake, I guess you’d have to travel to a distant world where it didn’t even happen.”
“But then you’d be forcing your failure on a version of you that didn’t deserve it,” I said.
“If our research continues to develop, I imagine we’ll reach that point eventually.”
“That’s why we need legislation. Even now, our superiors are campaigning for it.”
“I know what you mean. After all, who would be at fault if I, say, committed a crime in this world and went home afterwards?” she asked.
“Between neighboring worlds, most likely both of your selves would commit the same crime, anyway. But when it comes to 10 or 20 worlds apart, it’s not so clear-cut. And if it’s 100 or 200 worlds apart, the victim could be framed for the murder of someone they don’t even recognize.”
“I really doubt anyone’s shifting 100 worlds away completely by chance… Ack!”
Just as our tangents were spiraling out of control, like always, Kazune reached for her wine cooler without looking and accidentally knocked it over onto the floor.
“Oh, I’m so sorry!”
“Nah, it’s fine.” Grinning, I mopped up the mess with a tissue.
As I did, she cocked her head in confusion. “Wait, did I really put it there…?” Then she looked at her IP band. “Oh!”
“What’s up?”
Wordlessly, she showed me the LCD screen: 000.
“Oh, hey, welcome back,” I said.
“Thank you. Goodness, the transition really is seamless.”
I hadn’t noticed anything visually different about her or heard any hiccups in the conversation, so I truly had no clue when they switched back. She must have set her drink down in a slightly different location in the other world, and since she didn’t notice anything amiss, she must have been having the exact same discussion over there. Close-range parallel shifts caused little accidents like this all the time.
After I finished cleaning the floor, we looked back at each other.
“Well, I’m home now, so shall we…continue?” she asked sheepishly.
“No, I’m not really in the mood anymore.”
Laughing at ourselves, we let our first time end in failure. Ultimately, we made up for it less than a month later—though we kept our IP bands on and checked periodically, just in case. It was something of a stressful experience all around.
In summary, this was a major question brought about by the progress of imaginary science: were our parallel selves still us?
Thus far, the world had yet to find an answer.