Archive of Our Own ^beta

Chapter Text

The first clue that something’s wrong is when Deku’s chair is empty in homeroom on Monday morning. The next clue is when Aizawa trudges into the room, looking somehow even more tired than usual, with a tiny, green-haired toddler in tow.

———

“It should be apparent,” Aizawa starts, “that Midoriya encountered a quirk accident on patrol for his internship last night. He’s fine, as you can see, he just happens to be four-years-old right now.”

Katsuki stares so hard his eyes nearly fall out of his head. It’s like looking back in time.

“We’ve questioned the quirk wielder,” Aizawa continues, “and he assures us it will wear off in forty-eight hours. That means some time tomorrow just after midnight. He also says Midoriya will be able to remember everything that happened while he’s small, so there’s no point in having him miss class today and tomorrow. He will not be participating in our combat practice, of course, but he’ll come and observe.”

Yaomomo raises her hand and when Aizawa nods at her, she asks, “Is the age a parameter of the quirk as well?”

“As the quirk holder explained it, Midoriya’s been reverted back to a time before he experienced his first real trauma. So, I suppose...” Aizawa looks down at Deku and puts a hand on his unruly curls, “he’s been reverted to the most innocent version of himself.”

Katsuki frowns. The exact age Deku learned he was quirkless. That’s probably why he’s currently four-years-old. He hasn’t yet experienced the trauma of having his hero dreams shattered.

“So cute!” Uraraka exclaims, clasping her hands together gleefully.

Deku grabs Aizawa’s pant leg and ducks behind him.

“Is he...” Uraraka frowns. “On the inside, is he Midoriya now or then? Because he looks like he doesn’t recognize any of us.”

“He is as he was at this age, so he currently doesn’t know any of you, except for Bakugo, probably.”

Aizawa gestures at him and Katsuki stiffens in his seat. Huge, leaf-green eyes track over to him and he watches the wheels turn in little Deku’s head.

“Kacchan?” he asks quietly.

Katsuki doesn’t answer him. He just glares at the miniature trip down memory lane as Deku’s eyes get wider and wider and wider, recognition dawning as his little mouth drops open.

“Kacchan, you’re all grown up!” little Deku exclaims, “How’d you get so big?”

“Always been bigger than you, shrimp,” Katsuki scoffs.

Deku comes out from behind Aizawa and, to Katsuki’s dawning horror, runs right at him. When he gets to the desk, he bodily throws himself onto Katsuki and suddenly he’s got a lapful of smiling, giggling, baby!Deku.

“What the fuck, Deku!” Katsuki yelps.

The tiny, freckled face twists into a frown, brows drawing down. A toddler’s approximation of an ‘angry face.’ An expression mimicked before they fully understand how to use it. It would be comical except for what Deku says next.

“That’s not my name, Kacchan! It’s Izuku! EE-ZOO-KOO.” He draws out each syllable as he corrects him. “And you shouldn’t say the F-word. Auntie Mitsuki will spank you again!”

Katsuki’s face burns almost as hot as his quirk when half the class snickers. He’s sure he must be bright red.

“Oi, shut the fuck up!” he snarls at them.

“Kacchan!” Deku, or rather Izuku, reaches up with both chubby hands to mash his cheeks. All Katsuki can do is blink in surprise. “Stop saying bad words!”

This time the class bursts into full-on, raucous laughter.

“Get the f—Get off’a me!”

Katsuki pushes those tiny hands away from his face. He pops off a few explosions in the palm of one hand, mostly just to let off steam. Bright eyes zero in on Katsuki’s hand and he realizes his mistake too late. Izuku is mesmerized rather than intimidated like he should be.

“Is that your quirk now?! It’s so much bigger than the fireworks!”

Izuku snatches his wrist to have a closer look and Katsuki’s barely able to curl his hand into a fist and force the explosions to stop before he singes off tiny eyebrows.

“Oi! That’s dangerous!” Katsuki yells.

Izuku looks up from his hand with an angelic smile and says, “Kacchan would never hurt me.”

Any response dies in the back of his throat at the look on Izuku’s face. Katsuki swallows thickly and realizes how quiet it suddenly is. He looks up to find the entire class staring in silent disbelief. Izuku doesn’t seem to notice anything wrong, still examining his hand like it hadn’t just been inches from burning his nose off.

“Ok, that’s enough,” Katsuki says.

He lifts Izuku off his lap and sets him on the floor.

“Hey!” Izuku whines, “I wanna sit with you, Kacchan!”

Katsuki is about to snap when Aizawa saves him. “You can’t sit on Bakugo, Midoriya, he has to pay attention in class. But you can sit behind him. That’s your seat right there.” He gestures to the desk behind Katsuki.

Izuku follows the motion to the empty desk and his face lights up.

“Mine? Really?? Yay!” he exclaims as he scrambles around Katsuki’s desk to his own. He jumps up into the chair that’s definitely too big and grins from ear-to-ear as he clasps his hands on the desktop.

Iida raises a tentative hand.

“Are you sure it’s ok for him to stay here with us?” Iida asks, “Wouldn’t it be... safer and less upsetting for him to go home?”

“Well...” Aizawa scratches his chin, “Probably, yes. It would be easier all around for Midoriya to be sent home to his mother. We did contact her to let her know what happened and she was understandably concerned, however, we recommended keeping him here anyway... This is a learning experience for everyone.”

Iida makes a confused face and Aizawa continues.

“Quirk accidents are going to be a normal part of your Hero lives. You won’t just have to deal with momentary or immediate inconveniences, but also with prolonged fallout from them. When these things happen—because they absolutely will happen, to every single one of you—” Aizawa looks at them pointedly, “You will need to have failsafes in place to help you handle them. You’ll need to rely on classmates and teammates and partners to help you as well. So... we’ll be taking care of a little Midoriya until he’s himself again. I’ll expect you all to help out, although... sorry, Bakugo... the bulk of the work will likely fall on you.”

“What the h— Why me?” Katsuki protests, “I ain’t no—”

Aizawa hold up a hand. “It’s not like you’re going to get a lot of say in it. He is four-years-old and you are the only person he even remotely recognizes. It’s only logical that he will latch onto you, so get used to the idea right now.”

Katsuki sputters and crosses his arms.

“But like I said,” He turns back to the rest of the class. “you will all be expected to help out and make sure that Midoriya in his current state doesn’t experience any undue stress. Now, let’s start today’s history lesson...”

The class goes on like normal. Well, mostly normal. Izuku is marginally more disruptive in this form until Aizawa breaks out a pack of crayons and some construction paper. Seriously, he really is prepared for this, like he’s dealt with it a million times before.

Izuku, for his part, is actually able to participate in class. Their classmates seem to be thoroughly impressed, cooing and clapping when Izuku enthusiastically waves his hand in the air and answers a question correctly. Katsuki just rolls his eyes because he knows better. Even at this age, Izuku was a hero-nerd. He had facts of different heroes and hero history memorized practically from the womb, happy to share them with anyone and everyone from the moment he learned how to string words into sentences.

———

By the time morning classes are finally over, Katsuki is itching to get on the practice field. He shoves his books and assignments into his bag, aiming to be first into the locker room. In the corner of his eye, Uraraka approaches Izuku at his desk.

“Izuku-kun?” she catches his attention with a smile, “I’m Uraraka Ochaco. You can call me Ochaco-chan if you want. Would you like to walk to the gym with me?”

She holds out a hand and Izuku eyes her warily as he leans away.

“Um...” Izuku looks down and then up again. Katsuki is already out of his seat and slinging his bag over one shoulder. “I wanna go with Kacchan.”

“Hah!” Katsuki barks, “Forget it, pipsqueak. You’ll only slow me down!”

“No I won’t!” Izuku juts his little chin out, “I’m super fast!”

Katsuki scoffs. Uraraka tries again.

“Come with me, Izuku. Show me how fast you can go!” she tempts him.

“No!” Izuku snaps, “I want Kacchan!”

Aizawa slides over and blocks Katsuki’s exit. “Problem?” he enquires.

“Nope,” Katsuki growls as he tries to get past the teacher.

“I can make this a grade if that’s what you need,” Aizawa shifts to block Katsuki again.

“Are you kiddin’ me right now?!”

“Not even a little.”

Katsuki looks from Izuku’s angry little face to Aizawa’a passive but somehow also angry face. He lets out an exasperated roar that makes Izuku jump in his chair.

“You’d better keep up!” he yells at Izuku.

“I will, Kacchan!” Izuku smiles.

“You can leave your crayons and paper here, Midoriya. We’ll be back right after. I promise no one will touch them,” Aizawa tells him.

“Okie!” Izuku says as he jumps from his seat.

Katsuki is already turning away when he feels a tiny hand curl around two of his fingers. He looks down to find Izuku beaming up at him. All bright teeth and blinding delight. He wants to snatch his hand away, but Aizawa is still watching him expectantly. Katsuki grits his teeth and walks fast, practically dragging Izuku along beside him, little legs moving a mile-a-minute to keep up.

The next two days are going to be a fucking nightmare.

Chapter Text

When they get to the gym, little Izuku is clearly winded and Katsuki feels momentary satisfaction. Serves him right for ever thinking he could keep up with Katsuki, especially in this state. He’s so tiny. Even at this age, he was small for four-years-old. People used to mistake him for three or even two until he’d open his mouth and produce full, coherent sentences. Katsuki guesses he never really appreciated that because he was almost as small, even if he was closer to average for that age. Now that he’s older, Izuku’s size is so starkly off, he can’t help but notice.

Before he can shake the brat and bee-line it to the locker rooms, Katsuki sees All Might waving him over at the entrance. Reluctantly, he changes course to meet their shared mentor.

“Hello, Young Bakugo! Thank you for bringing Young Midoriya!” All Might greets.

Katsuki snorts in response and mutters, “Not like I had a choice.”

Little Izuku fists Katsuki’s pant leg and ducks behind him.

“Hello, Young Midoriya!” All Might booms as he bends to Izuku’s level. “You don’t know me but I’m one of your teachers here. You can call me Yagi-sensei.”

All Might smiles, eyes crinkling at the corners. Izuku doesn’t answer, just buries his face in the back of Katsuki’s thighs and peeks through his legs.

“Oi!” Katsuki yelps, “Get your head outta my—”

“I have a present for you!” All Might cuts him off and pulls an action figure of himself from behind his back as he winks. “I hear you’re a big fan.”

Little Izuku lights up like he hadn’t just been trying to hide somewhere up Katsuki’s ass and bounces out from behind him.

“Yes! I love All Might! I’m going to be a hero just like him someday!” Izuku exclaims.

All Might chuckles as Katsuki scoffs. If only he knew.

“The big kids will be engaging in combat training. Would you like to sit with me and watch?”

Izuku looks from All Might to the toy to Katsuki. If this little shit thinks he’s going to ride around on Katsuki’s back while he’s trying to pummel one of their classmates, he’s got another thing coming. Katsuki scowls, about to open his mouth and tell the brat that he’s not a babysitter when Izuku surprisingly agrees. Katsuki assumes it has more to do with the toy than anything else. All Might is definitely the way to Izuku’s heart at any age.

“Um...” Izuku ducks his head bashfully, “...ok.”

All Might holds out a hand and Izuku takes it. He glances over his shoulder at Katsuki as he’s led into the gym. Katsuki just scowls and walks away to freedom.

———

Katsuki’s the last one into the locker room and that only puts him in a worse mood as he bangs his locker door around, yanking his costume on as aggressively as possible.

“Dude, you ok?” Kirishima asks with a cautious half-smile as he buckles and adjusts his belt.

Katsuki feels the urge to deck him. He hopes Kirishima is his sparring partner today, he really wants to go to town without worrying about being reprimanded for unnecessary roughness with a classmate. Kirishima’s the only one who can take it from him. Well, Kirishima and Deku, but with one option down, he has to make do.

“Just fuckin’ peachy,” Katsuki snarls as he slams his locker shut and goes to the equipment cage for his gauntlets. “Always wanted a useless sidekick to hang off my back.”

Kirishima scoffs. He fucking scoffs. Katsuki is going to hand him his ass for the next forty-five minutes.

“Aren’t you bein’ a little overdramatic?” Kirishima asks.

Since when does he know such big words? Fuck Mic and his ability to teach grammar to neanderthals.

“Oh, I’m so sorry—” Katsuki turns on him and Kirishima holds up both hands in preemptive surrender. “—that I’m not jumpin’ for fuckin’ joy over having to babysit a tiny, even-more-useless Deku for the next two days!”

“Don’t be like that...” Kirishima tries to calm him, but Katsuki can only feel himself getting more annoyed. “Midoriya’s one of the strongest people in our class and you know it. He just had an accident. You can’t blame him for bein’ useless right now! He probably doesn’t even have his quirk yet!”

“Easy for you to fuckin’ say. You’re not the ‘chosen one’ or whatever...” Katsuki growls.

“Honestly, I though you’d be happy to show off. Imagine the look on his face when he sees what you can do.”

“Like he doesn’t already fall all over himself about it...”

Katsuki turns back to the cage for his gauntlets. Kirishima following him in to retrieve his shoulder pads. Katsuki’s just bending down to pull his items from the rack when a body collides with his back and he almost falls over.

“Kacchan’s just upset he can’t use his favorite punching bag!” Kaminari chortles over his shoulder.

“Die, you fuckin’ waste of space! Get the hell off’a me!”

Katsuki bucks him off and Kaminari lands on his ass hard enough to hurt. He’s rubbing at what’s sure to be a nasty bruise as Katsuki zeroes in on him, intending to beat him senseless right in the locker room.

“Bakugo!” Iida calls out, “Language, please! And wait until we get to the training grounds to attack your classmates!”

“C’mon, dude!” Kirishima exclaims cheerily as he hooks Katsuki’s arm and drags him away. “We’re gonna be late for class and you know Aizawa’ll make us pay for it!”

———

Kirishima is not Katsuki’s sparring partner at Gym Gamma. Instead, of all people, he’s paired with Koda. Cementoss creates a general terrain for the day and Katsuki shuffles irritably to the designated battle area for the two of them. Koda follows, also looking less than enthusiastic.

They square off to wait for the signal to begin and Koda signs, <<Please don’t hurt the animals.>>

Katsuki scoffs and looks away. Of course he’s not going to hurt the animals. Does Koda think he’s some kind of monster? Not that Koda’s concern isn’t understandable. The first time they sparred earlier in the year was in a wooded area. Koda called several squirrels to swarm him and Katsuki reacted as he normally would, with detonations. One squirrel lost a tail and another had to be run over to Recovery Girl with second degree burns.

They were both reprimanded, Katsuki for injuring innocent third parties and Koda for being reckless with the power of his quirk. Aizawa had been livid. What if they’d been fighting villains? What if Katsuki came up against a villain controlling civilians or using people as human shields? What if Koda fought a villain that didn’t care if any of his animals were hurt? Would he just keep sacrificing them to win?

<<Whatever.>> Katsuki signs back.

Koda keeps having some kind of anxiety about his non-answer, looking around to find Aizawa and probably request a different partner.

“Hey!” Katsuki snaps and Koda looks back to him. Jerkily, he signs, <<No hurt.>>

That seems to appease him and Koda relaxes into a fighting stance. Katsuki, on the other hand, can already feel the unsatisfied itch of a mediocre session. He’s going to have to hold back. Use some finesse and think harder about the size, magnitude and direction of his explosions.

Fucking snore. He’d rather just blow some shit up.

When Kirishima put the idea in his head that he could show off in front of a little Izuku, he’d almost thought it could be worth that morning’s shitshow. So much for that.

Katsuki squares up and assesses the current situation. The rest of the pairs are almost in position so it shouldn’t be long before Aizawa gives them the go-ahead. They’re inside, which puts Koda at a disadvantage. He can’t easily call up anything because even though Gym Gamma is sprawling, it’s still an enclosed facility. There’s really only one creature he’s sure to be able to talk to indoors.

Bugs.

Katsuki really hates it when Koda talks to bugs. In fact, the entire class hates it, including Koda himself. But if he’s going to be a Hero, he needs to rely on the resources at his disposal. Katsuki can respect that, even if it’s fucking disgusting.

From across the gym, Aizawa raises an air-horn, giving one short blast.

Immediately, Katsuki launches himself forward with twin blasts, skating across the ground as his boot scrape the concrete. Koda dodges. For such a big guy, he’s gotten quick at avoiding hits. Katsuki would be impressed if it didn’t piss him off so much. This is the other reason he hates fighting Koda. He never engages head-on.

With a snarl, Katsuki stops himself, feet planting as he skids to a halt. Raising both hands, he lines up his fingers and palm for his AP shot.

Even as he dodges again, Koda is muttering under his breath. There’s a crawling sensation at Katsuki’s ankles and he hears Izuku let out a horrified gasp followed by an “Ew!”

Katsuki absolutely does not look down. He’s learned from experience that it’s better not to look when you’re fighting Koda. Instead, he aims a quick blast at the ground, at a wide enough angle to sufficiently miss singing anything on his legs. His costume is flame retardant but the centipedes and beetles currently trying to scale him like a building, are not. The blasts propel him into a high hop. Mid-air, he shakes both legs out and the crawling sensations dies away. When he lands, the impact shakes loose the rest and when the feeling doesn’t come back, he figures they’re scared off for now.

“Wowww, Kacchan!” little Izuku marvels from the side lines, as if that was anything special.

Katsuki launches himself at Koda again, this time in a spin. Koda has more trouble dodging this time, and when one of his hits lands, Katsuki grins maniacally as he opens a palm and detonates a blast right against Koda’s shoulder. The bigger boy stumbles away with a yell, clutching his arm.

“Bakugo!” Aizawa’s voice carries warningly across the gym, “Watch it.”

With a scoff, Katsuki doesn’t take his eyes off his opponent. As if he doesn’t know.

Their spar goes on and Katsuki wears Koda down. Like he thought, Koda doesn’t put up nearly as good a fight as Kirishima or Deku or even Ashido would have. Koda just isn’t that kind of melee fighter. Not for the first time, Katsuki thinks that, as a hero, Koda isn’t suited to this type of work. Maybe he’ll be underground, working in espionage. Or maybe he’ll be one of those heroes that doesn’t fight at all. Instead he’ll go off and save the rainforest or something.

Their sub-par fight doesn’t deter Izuku from yelling encouragement and compliments from the sidelines though. There’s a constant stream of babble puffing up Katsuki’s chest.

“Kacchan is the best!”

          “Kacchan is sooo cool!”

                  “Kacchan is amazing!”

Damn straight he is.

Katsuki dodges a slow punch and spins around to get Koda in a headlock. Just as he’s about to crow “Game over, blockhead!” he feels a slither up his spine. It doesn’t matter though. Koda can send all the centipedes and worms he wants. He’s lost and Katsuki’s won.

Until he hasn’t.

Just as Katsuki gets his arm around Koda’s neck, something darts up to wind around his eyes and Katsuki can’t see. He howls in indignation and Koda ducks away. Katsuki is too annoyed to be careful as he reaches up to grab the snake around his face and whip it off. Where the hell was that thing hiding in here?!

It’s all the distraction Koda needs to sweep his legs and get Katsuki on his back.

“Get up! Get up! Kacchan, get up!”

Katsuki can hear Izuku screaming and he’ll be damned if he’s going to let Koda, of all people, beat him in front of Izuku so Deku can remember later.

As Koda goes to pin him, he twists and launches his legs off the cement, bringing them up to lock around Koda’s head and arm. Koda yelps and Katsuki roars, rocking back down until finally, he’s on top of Koda, pinning him to the ground. Koda stares up at him wide-eyed as Katsuki holds a glowing hand to his face.

“Give! Give!” Koda whispers frantically, tapping a hand on Katsuki’s thigh.

With a tsk and a scowl, Katsuki releases him and stands. He doesn’t bother offering to help Koda up.

———

By the end of the training session, little Izuku has fallen asleep on the bench, head pillowed in All Might’s lap. How he could’ve done that is anybody’s guess considering the various screams and explosions happening around him.

Katsuki sidles over and grins side-ways at All Might.

“Too bad you can’t pop into muscle-form anymore. Pretty sure he was potty-trained at this age, but he’d probably shit himself stupid if he knew who you really were.”

“Young Bakugo! I hope you’re watching your language around Young Midoriya here!” All Might chides.

Katsuki just scoffs.

When All Might looks back down at the sleeping kid, it’s with a wistful expression.

“Seeing this little face light up would be the highlight of my day,” All Might sighs, “but alas, that time is done and I fear it would only confuse and upset him to try to explain it anyway.”

Katsuki’s smile drops, looking from All Might to Izuku, eyes closed and little mouth gently parted against All Might’s leg. One hand is still curled possessively around the action figure. When Katsuki recognizes the unfamiliar sting of disappointment, he frowns harder. Does it... bother him that little Izuku doesn’t get to see that? That he doesn’t get to experience the unreal joy of meeting his idol at this age? Not that it would matter in the long run. When he turns back to Deku, he’ll know that he always knew who Yagi Toshinori really was and it won’t matter. There’s a little niggling thought in the back of his mind that stays with him though. Maybe he’s also a little disappointed that he doesn’t get to see that kind of joy on Izuku’s face.

“He was such a sweet, happy child,” All Might remarks quietly, “Not like the neurotic teenager we all know so well.”

Katsuki shrugs to avoid replying. It’s true. Not that he doesn’t remember what Deku was like at this age, it’s just that he doesn’t really think about it. Without a word, he turns away and stalks to the locker rooms.

———

After showering and dressing in his uniform again, Katsuki leaves the locker room to find Izuku awake again. He’s relieved to also find he doesn’t have to haul the kid over to lunch. Instead, Shoji ends up carrying him as Izuku babbles a mile-a-minute about all of his arms, jabbering excitedly about Shoji’s quirk and how amazing a hero he’s going to be. His little eyes shine.

When Izuku doesn’t turn those shining eyes on him once on the walk to the lunch room, Katsuki refuses to acknowledge the second pang of disappointment that morning.