Work Text:
Universal wavefunction theory dictates that when a problem has more than one possible solution, they are not alternatives, but simultaneous outcomes.
For instance: when a boy tells you he loves you, there are many responses, but mostly two: acceptance or rejection. These seem to be contrary possibilities, as if one ought to be rendered impossible by the other’s eventuality.
Everett-DeWitt theory posits that a new universe is created with every choice, every juncture. It says that all possible outcomes must occur, and at the point of divergence, the universe splits itself.
One Katsuki, now two.
Deutsch-Schrödinger theory says that there are many identical universes, filled with many identical boys in love with another boy, and they remain identical up to the point where he confesses. Then in some universes, you reject him, and in others, you accept him. From that moment on, the paths are changed from the point of common history.
Infinite Katsukis.
All this to say that in one universe, you probably love him back.
•
Deku is your soulmate, and maybe that’s why you hate him.
(You don’t, not really. You even admit it to yourself, and him, a decade later, when you’re sick of playing at being a boy-king. He sort of smiles at you, too-kind and too-forgiving as always, and nods, like I know, like that’s that.
And maybe it is.)
But even at sixteen, you don’t love him.
Not the way he wants.
(He tells you, once.
“Kacchan, I – ” And it’s halting, the way it’s not meant to be. You’re not meant to doubt how your soulmate responds, but maybe that’s the one good thing about your decade of cruelty. He’s accustomed to your rejection. He’s not going in blind, banking on acceptance.
You know what he’s going to say. Not in specific terms – you’re not a goddamn psychic, even if Deku is as predictable to you as the tides now – but in broad truths. You know him, after all. He’s never been able to lie to you, and he’s never really tried. Every inch of him has always wanted to love you – like he’s supposed to – and even if that’s changed from love like an open hand, seeking friendship to love like an open hand, offering forgiveness, it’s never wavered in its steadfastness.
“Kacchan, I love you,” he says, and it’s firm. Somewhere inside, you’re proud of him. More of you is trying to square with the weight of his truth.
You’re not proud of it later, but for a moment, you think about it. You consider whether you owe it to him to try, to lie. You’ve pushed him away your entire life, and now, when it’s the one love he’s always meant to be able to count on, you’re going to do it again.
It might be the worst thing you’ve ever done. But there’s nothing in you that knows how to lie about this. And you don’t know what would be more unforgivable: if you lied about this, or if he let you.
You decide the only kindnesses you have left to offer him are these: the truth, and not having to make that choice.
“I’m sorry,” you say. You’ve said it to him twice in recent memory; once as an apology for the last ten years, and now as an apology for the rest of them. “I – You’re a fuckin’ constant. I dunno who I am without that. But – it’s not like that. Not for me.”
Deku gives you that smile he gets sometimes, like he’s gonna find something good about something that sucks, like you could break his arms and he’d still find a way to be happy just because you were there.
“That’s okay,” he says, even though it’s not. He doesn’t take it back, doesn’t apologise, doesn’t do anything to make the weight of everything he feels any less. Which is fair enough. He’s shouldered enough for the two of you.
Maybe it’s only right that it should be your turn now.)
•
Todoroki Shouto is the most annoying person you’ve ever met, probably.
“You used to say that about me,” Deku says, snorting a little. You’re in his dorm room because the goddamn Half’n’half fucker lives on your floor, and you think you might actually explode if you have to see him again today. There’s no scientific proof for the theory of spontaneous human combustion, but maybe science just hasn’t gotten their hands on Todoroki Shouto yet.
“I was right,” you say, loathe to admit you’re ever wrong, before following it up with: “Anyway, this is different. He thinks he’s better than me.”
(You used to think that about Deku too. That he thought he was better than you. The difference is, with Deku it was because he always gave you so much fucking pity. Tried to be kind even when you didn’t know how to see it as anything but a honey-slicked dagger.
Todoroki Shouto definitely doesn’t pity you. In fact, you’re not sure he even cares about you, meaning acknowledges as a person who matters.
It cuts deeper than you want to admit.)
“Hmm,” is all Deku says, which is unhelpful as all fuck. You tell him as much, but he just shrugs.
You resolve to beat him at MarioKart to feel better about it.
•
People misunderstand Schrödinger all the time.
How can a cat be alive and dead at the same time? they ask, not realising that was his entire point.
Edwin Schrödinger came up with the most elegant denouncement of the Copenhagen interpretation maybe ever, and a century later, people are still telling the story wrong.
Copenhagen interpretation says that quantum superposition collapses upon observation. The cat is alive-and-dead until you check, upon which it is decidedly one or the other. Superposition – the state of being two different things at once – can only happen out of reach, and then it self-implodes.
It’s like liminality, you tell Kirishima once. That space between, where something could be fuckin’ anything – you’re waiting for the elevator, and you dunno if it’s going up or down, until you look at the light. Until then, it could be both.
Kirishima frowns. But it’s definitely one, he says slowly. Like, even if I’m not looking at it, it’s still up or down, right?
Exactly what Schrödinger was getting at, you say, triumphant. Fuckin’ crazy to think the truth changes only when we look at it. ‘Course the cat’s not both dead and alive. Just maybe whatever he is here, he’s something else in another world.
Kaminari puts his head in his arms and groans. There are other worlds? I hate physics, he mutters. More cats, less theory.
It’s funny, the kind that doesn’t make you laugh, that Schrödinger’s name became synonymous with the very paradox he was exposing.
That’s the problem with people. You can’t control what they’ll take in, what seeds will germinate, what truths will be laid wayside.
This story would be a lot neater if you could.
•
“Can you hurry up and fall in love with someone else,” you complain. It’s probably not fair. It’s definitely not kind.
But Deku just cracks a wry smile. “Working on it,” he says, halfway between a joke and an apology. That’s the closest he ever gets to paying you back in kind, when he sounds like that. Breaks your heart, just a little.
You knock your shoulder against his, your version of halfway between a joke and an apology. He knocks it back, meaning he doesn’t need either.
•
“Hi,” Todoroki says, sliding into the seat next to you.
You blink at him, then look around in disbelief. Yep. Just like you thought. At least forty empty spaces, all places Todoroki Shouto could have chosen to exist in.
And yet, here he is. World’s most annoying arrangement of atoms, with hair falling into his eyes as he pokes experimentally at his laptop power button.
“What are you doing?” you demand a moment later.
He blinks at you. “Sitting,” he says, then returns to frowning at his laptop. He presses the button no less than three times before you snatch his wrist.
“Give it a fuckin’ second,” you grumble, letting go of him so you can hold the button down. One, two, three.
The screen lights up, and so does Todoroki.
“Thanks,” he says, lips tugging up at the corners like the world’s most useless attempt at a smile.
It still feels like an electrostatic shock.
“Yeah, whatever,” you say, then, to make yourself feel better: “Get fucked.”
He just blinks at you, tilting his head a little, and you have the fleeting, horrifying thought of what Kaminari would say with that kind of set up. You’re pretty sure Todoroki would never, but the sudden image of him saying, with that stupid straight face, you offering?, has you ready to shove your face into the boards like Kirishima did to Monoma during the hockey match last weekend.
“You’re very hostile,” he says after a moment, but he doesn’t sound – aggrieved. If anything, he sounds a little amused. Thoughtful too.
“Yeah, well, if you’ve got a fuckin’ problem,” you begin, when he interrupts you (fucking audacity).
“I didn’t say that,” he says, a little quicker than normal. Not that you’re familiar with his speech patterns or anything.
He holds your gaze for a moment, two. You turn back to your notebook, glaring furiously at it. “Yeah, whatever,” you mutter, which isn’t anything. But you don’t tell him to go, not even when you feel his eyes on you throughout the lecture.
Probably you’re just feeling magnanimous because he’s finally acknowledged you, is all.
•
“Uraraka Ochako,” Deku says, shaping the name carefully in his mouth. He frowns at you. “She sounds nice, right?”
You roll your eyes at him. “How’s anyone meant to sound nice from a fuckin’ name, Shitty Deku? Don’t be stupid. Anyway, she’s doing a holiday programme for free. In her own time. Obviously she’s gonna be some bleedin’ heart nerd like you. Chill the fuck out.”
Deku throws a pillow at you. “You’re so unhelpful, Kacchan,” he grumbles. He still looks nervous, so you throw a chip at him. It bounces off his nose.
“Oi,” you say, holding up the controller. “Want me to kick your ass again?”
It’s a distraction. It’s the only gift you can give.
He glares for a moment longer, before his expression melts into a grin.
“I think you’ll find that last time I beat you,” he says, turning to the television to set up the game.
“Dream the fuck on,” you scoff, but you’re smiling too.
•
For instance, another version of you—let's call him Katsuki A, meaning Almost-you, meaning Another-you, meaning A-funhouse-mirror, because he has your face, but there’s something wrong if he’s choosing someone else—might love Deku back. Maybe in this version of your universe, Katsuki calls him Izuku and it means more than saying Deku, unbarbed, which is the most intimate truth you have now. Blunting the weapon you made. Offering fealty in a guilty mouth.
Maybe in this universe, Katsuki’s Deku doesn’t want to be called Izuku. Maybe in this universe, it’s you who is not loved.
You would prefer this, you think. It’s easier to think of you, unloved, than you loving someone other than Shouto and being happy about it.
•
“Do you have a soulmate?” you ask eventually. It’s a Tuesday evening, the lights are washing the wall with amber, and you haven’t been able to move your gaze for the past twenty seconds from the six centimetres of Todoroki’s skin revealed by his shirt riding up as he stretches his arms.
It’s the kind of question most people consider silly, but you’ve done the math, the readings. You know the theories. Not everyone has a soulmate, and even if they do, sometimes they’re like you. They don’t want them as anything more.
(Kirishima’s mother – the short one – studies the history of soulmates. According to her, soulmates haven’t always been considered romantic. Legend has it that the first ones to pursue romance were shunned by their peers, considering it a violation of the connection.
You wonder when that changed. Wonder if maybe humans as a people are too fixated on extremes, wonder if they’ve always just been meant to encompass the whole range of human relationships and instead everyone decided their way was the right one, and got mad at people for having something else.
Not like you can really throw that many stones, if it’s that, given everything you were as a child.
And maybe you’re just looking for a reason, an out to make it okay that you don’t feel the way you’re meant to.)
“Yeah,” Todoroki says after a long moment.
You swallow. Your heart lurches in your chest. You know these symptoms – not from prior experience, but how everyone who gets them knows them, even if they’re new, the same way everyone knows how to breathe the first time – and you don’t want them.
“You together?” you ask. It’s a little gruff. Maybe too much, maybe not enough. It’s hard to tell. The earth’s equilibrium feels whack now.
“No,” Todoroki says, and you remember how to breathe again. “He didn’t want me,” he adds on, and that same newly-reclaimed breath gets punched out of your lungs.
For some reason, you’d never considered that. The idea that Todoroki was the one who wasn’t wanted – it never occurred to you, and not because of any prejudices against people who weren’t loved by their soulmates like that. After all, you more than anyone know that sometimes it’s got nothing to do with what you think of them.
It’s just – you’ve never wanted anyone before, and definitely not the person you were supposed to. Then Todoroki Shouto dug his way into your chest, burrowing beneath your skin, and you were overwhelmed with it. Reluctantly, grudgingly, but undoubtedly.
“Oh,” you say. “Sorry.”
“It’s not your fault,” he says, looking a little wry. You don’t bother to tell him that you’re not sure if you’re saying sorry because you feel bad for him, or sorry that part of you is relieved by it. “I think it’s for the best, anyway.”
You blink. “Why?”
He looks at you thoughtfully. “I don’t think I would have been a very good boyfriend,” he confesses. “I’m not even sure I’m a very good friend, but Tenya is always there for me anyway.” He shrugs. “I want that most, I think. Anyway, I don’t know that I always know the difference.”
“Between what?”
“Friendship and romance,” Todoroki says. “All I knew was that he was the first thing that was mine. But – people aren’t like that. They’re not things.”
You think about what he told you once, late at night and squeezed into a bathtub together on Kaminari’s floor when looking for a breather from one of his parties, about his parents, his father. You swallow.
“No,” you say hoarsely. “They’re not.”
Todoroki looks at you, then smiles. That bright, unexpected thing that pops up without any warning and gives you a goddamn cardiac arrest at the best of times. You’ve never doubted your choice of major – you’ve never really doubted anything, except yourself, sometimes – until meeting him. Quantum physics does not adequately prepare you for Todoroki Shouto’s existence. You need a medical degree.
“Another good thing,” he says. “If Tenya and I were like that, I don’t think I’d have met you.”
•
“She nice?”
“Yeah,” Deku says, grinning big and bright. Hopeful, in a way you haven’t seen on him in years. Not in this big way, when his hope is too big for him to dare to put words to. He’ll never breathe a word of it, but you know it. You recognise it.
You may not love him like that, but you love him enough to know him to his bones.
•
“You’re the most irritating person ever,” you tell Todoroki Shouto the sixth time you ever talk, after two weeks straight of him sitting next to you in class. You’re not in class now, though. You’re in the ninth floor common room, where Sero and Jirou live, which is apparently a double fucking whammy, because Sero and Todoroki know each other from something-or-other class, and Jirou brings along her friend Momo, who turns out to be Todoroki’s Not-Girlfriend.
(It takes about three minutes for you to turn Not-Girlfriend into not girlfriend, which is roughly the same amount of time it takes Kendou Itsuka to catch Momo’s eye.)
“That seems improbable,” he says. “Very easily falsifiable. You should choose better hypotheses. That’s much harder for you to verify than for me to disprove.”
It’s a little troubling that him being a pedantic asshole about this makes you like him better.
“Don’t need to worry about that if I’m right, which I fucking am,” you parry. “You’ll spend the whole time trying to find someone more annoying than you, and fail, because they don’t exist.”
Todoroki raises an eyebrow. “There’s you,” he says, which makes Kaminari spit out his drink and Sero howl with laughter from across the room.
“You’re way fucking worse!” you exclaim, and if you lose hours to arguing with Todoroki Shouto – which turns into debate, into discussion, into him showing you photos of his favourite cats he spots around campus at 1:15a.m. when you’re barely managing to keep your eyes open – that night, it’s far from the worst experience you’ve ever had at your friends’ parties.
•
“How’d you know Iida?” Deku asks Todoroki once, and it makes you fucking itchy that they talk now, but the idea of them not is somehow worse.
It’s a fuck of a dichotomy you’ve worked your way into, but it is what it is.
“Oh,” Todoroki says, that stupid way he does. He’s currently failing at buttering toast. You would help him, but the level of incompetence is so staggering at this moment that you need some time to recover. “We’re soulmates.”
Deku drops his coffee mug. Actually, it’s your mug, and it shatters, so. Awesome.
“Fucking hell, Deku,” you mutter, then turn around to rummage through the cupboard behind you for the half-brush and shovel.
“Sorry, sorry!” he squeaks, but he’s still looking at Todoroki, not helping, which means it must be important. His expression is strangely – you don’t know. Envious, maybe.
“Oi,” you say, clearing your throat. They both look at you, and you nod at Todoroki. “Your inability to make toast is fucking painful, as is Deku’s shitty cup-handling. Go get some real fucking breakfast for the pair of you while Deku and I clean this shit up.”
Todoroki doesn’t even question it, just nods and wanders out the door.
The second he’s gone, you turn to Deku. “What’s that about?” you demand. “Thought you liked Uraraka.”
Which – you haven’t said. This is the first time you’ve put voice to it. You don’t know if it’s because you’re worried you’re reading into it out of desperate hope for it to be that for Deku, or because you don’t want to shatter any fragile solace he’s found there.
He squawks and goes red, but doesn’t deny it. “It’s – it’s – ” he stammers, before giving up, burying his face in his hands.
“Okay, the fuck?”
“I do,” he confesses to his hands. “I just – ” He looks like he’s struggling, as much as you can tell through his fucking hands.
“They’re not together,” you say, taking pity on him. His head snaps up, and you roll your eyes. “Halfie and your Iida – they’re not like that.”
They’re like us, you could say, but you don’t. You’re never sure if it’s salt in the wound.
Deku’s eyes widen, then brighten, and it makes your heart clench, in a good way.
Somehow it doesn’t surprise you, even though your entire life has been built around Deku trying to give you all the love you couldn’t accept. Maybe that’s it. He’s always had so much love to share, pouring it into gardens that drowned beneath his endless ability to give; maybe it’s not a surprise that there’s more than one of them.
“Go get ‘em, tiger,” you say, and he flushes scarlet.
“Kacchan!” he whines, but there’s that smile on his face that reminds you of when he was seven and proudly showing the entire class the dorky letter the Tooth Fairy wrote back to him. Embarrassed but pleased, like he’s giddy enough that he can’t contain it.
It’s not that easy, you know. Whatever this is won’t erase the years of everything else he endured, everything he dealt with while he was waiting.
But you hope that maybe it’ll be like how Todoroki feels, with Iida. Like maybe at the end of it all, it’ll feel right.
It’s a selfish thing to want, because it makes your life easier, but you want it anyway. You want it for him too. He’s always deserved it. You just can’t give it to him.
•
“Mm, Shouto,” you murmur, half-asleep as you nudge his shoulder with your head. “Turn the page, dumbass.”
He doesn’t turn the page. He does turn to stare at you, though, eyes wide and a little wondrous.
“The fuck?” you mumble. “You deaf now?”
“You said my name,” he says, and it sounds – awed, in a way that doesn’t make any sense, because you’ve called him Todoroki before – sometimes – so why –
Oh. Your cheeks flush pink. “Fuck,” you say. “I’m tired, shit – ”
“No,” he says firmly. “I liked it.”
You stare at him, open-mouthed.
“It felt safe in your mouth,” he says, like that’s not a fucking insane thing to express, like that’s remotely survivable to hear.
He turns the page.
You stay looking at him.
•
Everett-DeWitt theory says multiple versions of yourself must exist, born out of every instance for which there are multiple outcomes. It says there must be one version of you that chose Deku when the choice was offered.
You understand this, hypothetically.
In practice, you can’t believe there’s any world where you choose him. Where you choose a non-Shouto.
It has nothing to do with Deku, who you love even if you don’t love the right way, and everything to do with Shouto, who works his way into your ribcage so fundamentally that you can’t imagine how any universe could exist where your atoms aren’t in love with the shape of his.
Quantum entanglement means that two particles, no matter how far away from each other they are, remain linked. Some scientists posit that love is this: my sub-atomic particles recognise yours, are one with yours. My body recognises your body. This is a love story, played out on the smallest of scales, so minute that the eye cannot see. Intimacy transcends distance. Like recognises like. I, you, you, me.
If Deutsch and Schrödinger are right, and there are infinite universes, you think you may have to disagree with their theorem. You hope you can choose Shouto in each of them.
•
“Did you know,” you murmur, because for all his backchat about fucking falsifiability, Shouto’s a goddamn philosophy major, “that Schrödinger said there were alternate universes?”
Shouto, lying on the roof beside you, turns his head to look at you. You can see the stars reflected in his eyes. It makes your chest ache something fierce.
“Kind of,” he says. “It got mentioned in passing during an existentialism lecture. Is that what the cat was about?”
“Kind of,” you say, half-teasing, half-serious. “It was to point out that popular reading of superposition – saying that ‘cuz something has a few possible states, it exists as all of them at the same time until proven otherwise – was ridiculous. The cat’s not dead and alive at the same time, that’s fucking stupid. And if you look in the box and the cat’s still alive, obviously it’s never been dead as far as it remembers, but the theory meant that it was supposed to be both before anyone observed it as otherwise.”
“I hope the cat is always alive,” Shouto interjects, and you turn a little, laughing into his hair.
“You fucking would,” you say, but it’s fond. Long way from the most annoying person in the world, though you still stand by that when he’s being a stubborn fuck about something unexpected. “Anyway, the point is that microscopic theory has macroscopic repercussions – we’re not just particles, we’re people.”
“Mm,” Shouto hums agreeably. “Where do the alternate universes come in?”
“He says that if there are multiple solutions to something, they’re not just alternatives, they’re all true. Just in different universes.”
Shouto makes a noise as he absorbs this. “So,” he says, turning a little as well, so he’s staring directly at you. He bites his lip – just the tiniest of touches, for a brief moment, but it makes your pulse skyrocket – then takes a breath, saying, “If I kissed you, then in at least one universe, you’d kiss me back?”
There’s no breath in your lungs. There’s just Shouto, everything about him: the way he looks under starlight, the way his hair shifts in the night breeze, the feeling of his heartbeat pounding out of his ribs right into your own chest.
“Yeah,” you breathe. “Yeah, exactly.”
“And…” He sounds almost-normal, but there’s a quickening to his breath, a little tremor to his wrist, and it floors you, that he’s capable of being nervous. “And in this universe?”
You lean forward and press your lips against his, swallowing his tiny gasp. His lips are as soft as you thought they would be. There’s a tiny scar at the edge of his bottom lip, on the left, and it makes your brain go crazy, thinking about how he might have that in a thousand universes, or only in one, but it’s the one that matters most, because it’s the one that has your lips pressed against it, tasting it, tasting him.
“In this one,” you murmur, “I kiss you.”
“I hope they’re wrong,” Shouto whispers against your lips. He slides them across in a sweeping kiss, then tilts his head to try kiss you deeper. “I hope one thing can be the same in every universe, because I hope every Shouto gets to do this.”
God, your chest fucking aches.
“But I’m glad that it’s happening in this one, at least,” he says, pulling back to look at you a little better. His lips are red, like an imprint of you has fundamentally affected him. Your particles and his particles, uniting. Quantum entanglement, you think, half-deliriously.
“Me too,” you say, unable to bite back your smile before you lean in to kiss him again.
•
Hypothetically, there is a universe where he doesn’t love you, or you don’t love him back.
It’s not this universe, though, and that’s all that matters.