Chapter Text
It was a Tuesday after school. The sun was shining, the schoolyard rapidly emptying, and Deku was being fucking difficult.
Again.
Sparks lit in Katsuki’s palms. “What did you say, Shitty Deku,” he growled.
The little twerp’s eyes were wide, his shoulders trembling, but, as ever, he refused to back away.
“Mom wanted me to ask you to dinner tomorrow,” he said, voice quiet but clear.
Katsuki felt a familiar fire ignite in his chest, and the explosions in his hands grew. “We. Aren’t. Fucking. Friends.”
“I know,” Deku replied, lowering his eyes, but still he refused to move. Fuck, if it wasn’t the most infuriating thing, how he was so weak, but never acknowledged it—but yet never fought back. Katsuki didn’t truly know what he wanted out of Deku, if he were to be perfectly honest with himself—but whatever it was, it wasn’t ever what Deku did.
So, they were at an impasse. One that must have occurred thousands of times before, to be sure, but that never once quelled Katsuki’s annoyance, in all the six years since he’d gotten his quirk, and the loser trembling in front of him hadn’t. It was an anger that refused to die, but, since Katsuki was fueled by anger as a rule, this was something he was willing to live with.
“But we could be friends,” Deku murmured, and the dam holding Katsuki back cracked.
“Who the fuck do you think you are,” he snarled.
Deku just said nothing.
Katsuki scowled, but then smirked, raising a fiery palm.
Anger had an outlet.
Deku tensed, bracing for impact, one that almost came—
—before Deku disappeared in a puff of black smoke, Katsuki’s explosion scorching the brick wall behind him.
Katsuki’s heart skipped a beat, and he froze, staring at the empty space in front of him.
What the fuck?
Mind racing, Katsuki took a furtive glance around. What was that? Where was Deku? Was it villains? Katsuki had never been up close to a villain attack, and suddenly, he realized he really didn’t want to be.
Or, worse, had that—had that been Deku himself?—
—and then the black smoke reappeared, and a mass of green lightning came hurtling out of it, missing Katsuki by mere centimeters as it crashed into the schoolyard, digging a deep rut through the grass. Almost faster than Katsuki could comprehend it, the figure—it was a person, Katsuki realized—scrambled to their feet and launched themselves straight back where the black smoke had been, only to crash into the brick wall. Into, as in, they made a full body-sized crater in it, dust exploding everywhere.
Katsuki gaped and took a couple involuntary steps back. Suddenly, he wasn’t the most powerful person around. Not by a long shot. He hated how his heart began to pound.
He wasn’t scared. He wasn’t. Katsuki may have been eleven years old, but he wasn’t a fucking weakling.
As the dust began to settle, Katsuki kept an eye on the figure. It looked like a man, lean but tall and musclebound. The lightning had by now mostly subsided, but now and then a couple of sparks arced up and down the man’s body as he emerged from the wall, waving the dust away from his face. The whole theme with this man seemed to be green—green suit, green light, green hair. Katsuki squinted. He didn’t recognize the costume, which was strange, but it looked like a hero’s. Or, at least, he fucking hoped this was a hero, that he didn’t know for some reason, even though he could have sworn he knew all of them (he wasn’t a fucking nerd like Deku, alright, he just—he appreciated heroes, okay?). Otherwise, he was screwed.
“Some sort of teleportation quirk,” the hero(?) was muttering. “Black smoke. It’s the same color as All for One’s, but that manifested itself as more of a liquid-like substance. Still, it’s worth noting that it transported me somewhere important to me, so the villain must have personal knowledge they plan to use against me…”
Katsuki didn’t know what the man was going on about, but he wished he’d get on with it, because he was in fucking suspense here. Maybe he should say something? No, that would be an idiotic move—
Then the man saw him, and he froze, mouth open, as if Katsuki was the one who had just come fucking flying out of nowhere.
“Kacchan?”
Katsuki’s thoughts ground to a halt.
Only one person, only one, ever fucking dared to call him Kacchan, and that was the nerd who he’d been about to put back in his place. The nerd who’d been standing right there, fifteen seconds ago.
Katsuki’s eyes darted back to the man, only this time, he looked closer.
Same broccoli-ass hair. Same ridiculously huge eyes. Same open expression.
No, no fucking way.
The man recovered quickly, forcing on a blinding megawatt hello-there-random-citizen smile that reminded Katsuki, rather uncannily, of All Might, but that only made the damage worse, somehow. He was trying to backtrack, to cover it up, but there was no mistaking that stupid face.
“Deku?”
The man’s grin faltered, and an edge of panic creeped into his eyes. He looked like a fucking deer in the headlights. Katsuki’s stomach twisted at the confirmation, and his heart started pounding faster. Fuck, it truly was him.
He was a grown-up now, and distinctly un-quirkless, but it was fucking him.
Katsuki gaped. The hell?
The strange, older version of Deku seemed frozen for a couple moments more, as if debating something in his head, before his shoulders slumped, and he ran a hand through his hair. “This is bad,” he mumbled. “I’ve never time-traveled before, but if this quirk induced a time-travel concept in which the past can indeed be changed, instead of a fixed timeline, which must be the case since Kacchan didn’t know, and he’s not a very good actor—”
Katsuki didn’t know whether or not he wanted to roll his eyes, punch something, or scream. The muttering. The fucking muttering.
Fuck fuck fuck fuck—
Katsuki clenched his fists. Grown-up Deku. Hero. Quirks. Time travel? Super-strength—how the fuck did Deku get a quirk?
Hero Deku cleared his throat, and Katsuki’s eyes snapped back to him. Fuck, Deku looked so strong and confident and—and everything he wasn’t supposed to be. Katsuki had always been the strong one, the one who was going to be a hero, but this adult version of Deku—
—he looked exactly like the kind of hero Katsuki had idolized since he was in diapers.
Katsuki felt smaller than he’d ever felt in his life.
“Sorry, Kacchan,” Hero Deku said, with a weak smile. “I—um—” he faltered. “This isn’t ideal.”
“No shit,” was all Katsuki could think to say, and Hero Deku laughed suddenly, a big, joyful laugh, as though Katsuki had said something actually funny.
Hero Deku noticed the look on his face and clamped his mouth shut. “Oh, uh, sorry. You just—reminded me of your older self, that’s all,” he said, before wincing. “Oh dear. Time travel. I really shouldn’t say anything like that.”
Older me, Katsuki thought for a moment, but then his mind went blank again. He kept staring.
Hero Deku seemed to study him, pensive, before crouching down to Katsuki’s eye level. Something in Katsuki roiled with annoyance at the implication that he had to be talked down to—he was eleven, not three—but the feeling felt fuzzy, distant.
“Kacchan, can I ask you a favor?”
A favor. From him? What the fuck could Grown-up Hero Deku need from him?—but Katsuki gave a quick nod, anyway.
“Can I ask you where I am?” Katsuki gave a blank stare, and Hero Deku blinked. “Ah, that is, your Izuku? The one that’s the right age?”
Oh. “He disappeared,” Katsuki mumbled.
Hero Deku frowned. “Did it look like the same quirk? Black smoke?”
Katsuki nodded.
“Not good, not good,” Hero Deku muttered, chewing on his lip, before jolting, as if in realization. “A switch quirk,” he said, and his eyes widened.
He turned back to Katsuki and placed a hand on his shoulder. Katsuki tried not to flinch. “Kacchan, I know you don’t like me very much, but—I think the villain that did this was trying to hurt me. Younger me. If I’m right, he might be in the future right now, but I think I and my younger self will switch back soon. He might come back really hurt. Can you help him—me?”
Katsuki looked at his big, wide, sincere, Deku eyes. Fuck it, he wanted anything rather than to say no.
Maybe that’s why Deku had always infuriated him so much. Because Katsuki never could really want to hurt him.
“Okay,” Katsuki managed, and Hero Deku smiled, a look of relief on his face, and Katsuki felt a twinge of guilt at the idea that Deku might think he wouldn’t help him.
He could see why.
“Thank you.” Hero Deku paused, smile fading. “There’s something else I have to ask you, though.”
Katsuki waited.
Hero Deku fixed him in the eye, suddenly gravely serious. “Time travel is very dangerous. The smallest difference could change everything, and that could be really bad. Do you understand?” Katsuki nodded again, and Deku continued. “That’s why I have to ask you to keep all of this quiet. Don’t tell anyone—not the police, not your parents, not your friends, especially not me.”
“About your quirk?” Katsuki found his voice all of a sudden. He’d thought—well, he hadn’t known what to think, but maybe his Deku had just been hiding it, or it was dormant, or something—so wait, his Deku didn’t know?
Hero Deku gave a small grimace and looked down. “Yeah. Especially not that.”
Katsuki stared. Deku wanted a quirk more than anything, and Katsuki wasn’t stupid—the freak’s life would be a thousand times easier if he did have one. But here his future self was, practically begging him not to say anything—that one day, he wouldn’t be a quirkless loser anymore.
“Why? And how’d you even get a quirk, anyway?”
Hero Deku gave him a rueful smile. “Sorry, Kacchan, I can’t tell you that.”
Suddenly, Katsuki was angry—what, he was just going to show up, all hero-y out of nowhere, and he wouldn’t even let him know what the fuck was going on? He was big, he could handle it—
—but then the black smoke appeared all around Hero Deku, and Katsuki’s eyes widened.
“Please,” Deku said, voice still firm.
“Yeah, alright,” Katsuki groused, and then Hero Deku was gone.
For a long, terrible moment, Katsuki was alone in the silence of the schoolyard.
Then, all of a sudden, the black smoke came back, and Deku—his Deku—came stumbling out.
Katsuki hated how relieved he was to see the nerd, safe and sound—
—but then Deku collapsed, and Katsuki yelped in shock.
There was a knife sticking out of Deku’s side, blood leaking out at a rapid rate.
Katsuki felt the blood drain from his face. He wasn’t fucking squeamish, but this—
Damn it, Deku couldn’t die, Deku—
Katsuki choked down a sob and whirled around, looking for someone, anyone. He needed help. He—he usually hated needing a grown-up for anything, but—but Deku—
Katsuki’s feet took him into the school. He barely recalled yelling at a teacher to come do something, leading them back to where Deku was, the sirens of the ambulance, the police bugging him to find out what had happened. At first, Katsuki hadn’t been able to register anything, to let any image into his mind but Deku, bleeding out on the grass—
—but finally, when they got fucking annoying enough, Katsuki snapped. A villain attack, Katsuki told them, and he wasn’t fucking lying.
He just wasn’t telling them everything.
He was going to keep his word.
***
Katsuki sat by Deku’s hospital bed, the attack running through his head on repeat.
Shit, the nerd was supposed to live, according to the doctors, but he looked so weak and helpless—useless, like the name Katsuki had given him—like this, so much so he could hardly reconcile the picture in front of him with what he’d seen, earlier. Deku the fucking pro hero, with a powerful quirk and a smile to rival fucking All Might’s. It was fucking unbelievable—
—but at the same time, something in Katsuki didn’t doubt what he’d seen was the truth. The future. The more he pondered it, the more right it felt.
It was infuriating. Or, it should have been.
As angry as Katsuki wanted to be—he couldn’t fucking do it.
Oh, he wanted to be mad. Deku, the weakling, the extra, would somehow pull a huge quirk out of his ass, the lucky fucking bastard. He’d get everything he always wanted. He was going to go and take the profession Katsuki always wanted to do, too. Hero-ing was supposed to be Katsuki’s future, not Deku’s. The fucking nerve.
But then Katsuki looked back at Deku’s face as he slept, and he thought about how little Hero Deku’s face had changed. So kind, and open, and—trustworthy. Katsuki had met Hero Deku for all of two seconds, and he already had trusted him with his fucking life, no questions asked. He positively radiated a sort of safety, and comfort, and—it was disgusting. But undeniable. Deku had the fucking face of a hero.
This was the kid he punched the lights out of on a nearly daily basis.
All of a sudden, the thought made him sick.
Katsuki uncurled his palms and ignited several sparks, watching as they ran from his thumb, all across his fingers to his pinkie, and then around and back again.
Katsuki had something special of his own, though, and he wasn’t fucking giving up on it.
He looked back at Deku. “Alright, just fucking try it,” he grumbled, quiet enough that no one would hear him and kick him out. “But I’m going to be even better. You hear me?”
Nothing but the beeping of the heart monitor.
“Right,” Katsuki muttered, and he rose to leave, before pausing at the doorway and looking back.
Well, if Deku truly couldn’t hear him…
“Sorry,” he whispered.
Katsuki turned, opening the door as quickly as he could and making his escape, cheeks flaming.
Oh, fuck, he couldn’t believe he’d just done that. As he stood, his back to the door, though, he felt something release in his chest, something knotted and ugly and heavy.
Ugh, he'd been around Deku for too long. How fucking sappy.
Still. It felt… pleasant not to have to hate him.
Well, whatever—no one would know about today, anyway. Katsuki would make sure of it. Anyone who learned the secret would be fucking dead.
***
When Deku finally returned to school, Katsuki couldn’t stop himself from watching him, all day. He looked even more fragile after the whole ordeal, physically, but Katsuki was looking closer, and he could still see something of the grown-up hero in him, the same quiet, optimistic determination.
After class, Katsuki’s dumbass friends—or, maybe, allies was the better word—decided to swarm Deku, blocking off any escape and lobbing taunts and jeers—business as usual. Katsuki walked through them, straight up to Deku, and paused, looking him in the eye.
As always, Deku simply stood his ground. No offense, no defense. Just resignation and a sort of sadness.
Katsuki fought the urge to roll his eyes. Fucking infuriating.
Without a word, Katsuki turned on his heel and walked away.
Out of the corner of his eye, Katsuki watched as the extras all froze, or dropped their jaws, gaping like fucking trout fish.
“What are you fucking waiting for?” Katsuki snapped.
They followed him.
Katsuki didn’t look back.