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Aizawa was late.
There was no reason why he should be late, and that was what had everyone so worried. In his absence the class had broken up into groups, each loudly and animatedly sharing their theories on the situation. The prevailing opinion was an emergency call to deal with a villain attack, spearheaded by the more levelheaded members of the class, but about five minutes after Aizawa was supposed to show up and didn’t, a splinter group had broken off and started throwing out increasingly outlandish ideas. A full third of the class was now attempting to explain to Iida why it was perfectly reasonable to think Aizawa had been turned into a snail.
Katsuki, frankly, did not care.
“Get off my desk,” he told Kaminari, popping a finger against his knee as he sat on top of it.
Kaminari, to his credit, didn’t even flinch. He turned partially, propping a foot up on Katsuki’s thigh, then put it back when Katsuki shoved it off.
“Come on,” he said, nudging at Katuski. “You gotta have a guess.”
“I don’t give a shit,” Katsuki repeated for what felt like the millionth time, popping another finger against his ankle.
Look, it wasn’t like he didn’t care about Aizawa in general. He felt the itch of anxiety under his skin, a fear that hadn’t left him since the end of the war, the persistent conviction that anyone not in his sight was a body waiting to be found. An illogical part of him, the part that jolted him awake every night with the feeling his heart was stopping, thought all these worst case scenarios weren’t bad enough, even as the logical part of him said that if something had happened, someone would have come and told the class, or one of them would have found a news report.
It was just, well.
He was a little more worried about Izuku.
No one had seen him that morning, not even his floormates. Aoyama had heard someone coming in late and assumed it was him having been held up at his internship, but he hadn’t responded to any knocks on his door before breakfast. It wasn’t unheard of for him to sleep late after a long night, though it wasn’t by any means common, so Katsuki had tucked his portion of food into the fridge and promptly been lured off by Kirishima and Kaminari before he could go and check on him himself. Neither of them had been too worried, and Katsuki hadn’t given it a second thought until he stepped into the classroom and Izuku hadn’t been there either. The rest of the class was too caught up with Aizawa’s mysterious absence to notice, but the longer it went without any sign of either of them, the more Katsuki became convinced something very bad had happened.
“Hey,” he said, curling a grounding hand around Kaminari’s ankle. Kaminari looked at him, the toe of his shoe digging into Katsuki’s stomach in a way that was probably supposed to be annoying but was oddly comforting. “Do you -”
The door slid open.
Kaminari launched himself off Katsuki’s desk like a startled cat. The class scattered back to their seats as Aizawa trudged in, rubbing his face tiredly. Katsuki straightened up slowly.
Aizawa met his eyes. He pinched his lips together and nodded. “Midoriya is fine,” he said, and Katsuki licked his teeth and didn’t bother denying his worry. Aizawa sighed. “There was… a mishap last night.”
“Deku?” Uraraka said at the same time Kirishima asked “Is everything alright?”
The empty seat behind Katsuki burned. He flexed his fists.
Aizawa waved them off. “He’s fine,” he repeated. “A civilian lost control of her quirk while he was in the area. No one was harmed. He’ll simply need some extra help for a few days until it can be reversed, or it wears off on its own. He’s…”
The door slid open again. All Might inched inside, hands cradled carefully to his chest. He stilled as twenty heads turned to him at once, then smiled. Aizawa raised an eyebrow as he approached.
“It’s been agreed it’s best not to leave him alone,” All Might said quietly. Katsuki leaned forwards.
“I thought we also agreed he would be staying with Recovery Girl?”
“He doesn’t seem to like that.”
Flex, flex.
“Um, is something the matter?” Yaoyorozu’s voice was worried.
Their teachers seemed to suddenly remember they were there.
“Yes,” Aizawa began again. “Midoriya is simply -” A tiny green head popped out between All Might’s fingers. He sighed again. “Shrunk.”
Someone squeaked. There was a second of total silence, and then the class exploded.
“What?”
“Oh, he’s little.”
“What happened?”
“Is he alright?”
“How long will he be like that?”
“You can fix him, right?”
Dumbstruck, Katsuki watched as Izuku flinched and clapped his hands over his ears, ducking down into the cup of All Might’s hands. Without really thinking he stood and walked to the front of the class. All Might slowly separated his hands, revealing Izuku inside, clinging to his fingers as he huddled down with his back to the class. He was trembling.
Silently, Katsuki reached out. Izuku turned around as the shadow of his hands passed over him. He sprang up, his tiny face lighting up as he saw Katsuki. He scrambled over, clambering over Katsuki’s thumb and into his palm. He wasn’t as tiny as he looked in All Might’s hands, but to Katsuki he was still small enough that he weighed almost nothing, the brush of his hands and feet almost ticklish as he curled up again. Katsuki tucked him against his chest and returned to his seat, feeling a tug on the collar of his shirt as Izuku hoisted himself up to snuggle into his neck and shoulder.
“Enough,” Aizawa said. The clamor continued. “Enough!”
Izuku flinched at the sudden noise. Katsuki cupped a hand around him as the class fell silent. He listened with half an ear as All Might reiterated the quirk mishap, far more focused on how Izuku clung to him.
“Now,” All Might continued. “As you can see, young Midoriya is in no shape to care for himself right now. He’ll need a little help until he can be returned to normal. He can’t seem to communicate as usual, so it will be a big responsibility. Perhaps if some of you take turns?”
“We can -” Todoroki started, and Katsuki rushed to cut him off.
“I’ll take him.”
Aizawa looked at him, face blank.
“The whole time,” Katsuki clarified. Like hell anyone would be touching Izuku but him.
“Excellent,” All Might said, and that was the end of the conversation.
Izuku made it to the end of second period before his shaking got so bad Katsuki had to be dismissed. He carried him back to the dorms, still clinging to his shirt. Halfway to the elevator he stopped, suddenly remembering what had been bothering him so much all morning. Izuku's face was pinched as Katsuki held him out and squinted down at him. “Did you eat?”
His face furrowed even more. Katsuki repeated himself, but Izuku just shrank back.
“I don't know why I'm even asking,” Katsuki mumbled. “You can't even talk anyway, can you?” The second the words left his lips, he knew. “You can't understand me either, can you?”
He carried Izuku into the kitchen and set him on the counter. He poked him in the stomach and then pointed to the fridge. Izuku's face turned between them a few times, then he brightened and nodded. He pointed to his stomach and sat down, little feet swinging over the edge. Katsuki picked him up and put him further away from it, then opened the fridge. What the hell do you feed a ten centimeter tall human? He pulled out the plate he’d made that morning and examined it thoughtfully. Probably not the best option. He put it back and found an apple. Then, fruit and knife in one hand and Izuku in the other, he made his way to his room.
He watched Izuku eat with amusement, biting messily into a small chunk of apple as he sat on Katsuki’s pillow. He laid on the bed next to him with his hand propped up on his hand, chewing on his lip thoughtfully. He had no reason to assume Aizawa and All Might were lying that he wasn’t hurt or in danger, and he doubted they’d have let Izuku out of the infirmary no matter how big a fit he threw if they didn’t think they could fix this. Izuku seemed fairly content now that they were away from the noise, anyway. Katsuki apparently just would just have a very tiny boyfriend for a few days.
Might as well enjoy it, he guessed.
“You’re an idiot,” he said lowly, hovering a fingertip in front of Izuku’s face. Izuku dropped his hands and leaned into it, half of his face disappearing under the touch. “You know that? How do you always manage to get into trouble like this?”
If Izuku was his usual size, or at least capable of communicating, he probably would have taken offense to that. Katsuki could practically hear his “and how many times have I had to rescue you, Kacchan” anyway. Small as he was, though, Izuku only smiled at the sound of his voice and carefully climbed off the pillow to make his way wobblingly to Katsuki’s side, feet unsteady on the bunched up sheets. Katsuki picked him up and rolled onto his back, setting him on his stomach. He ran two fingers down his back as Izuku stretched out, all four limbs sprawling, not even reaching the sides of his chest.
“Don’t fall asleep,” Katsuki murmured, craning his head awkwardly to look at him. “I have homework. I will move you.”
He did not move him. He woke up an hour later to the ping of his phone somewhere by his head. In the haze of waking he forgot Izuku was on his chest until he rolled onto his side to reach for the source of the noise and he went sliding straight off, glaring up at Katsuki with a pinched, sleepy face as he pushed himself back up. Katsuki snickered.
“Sorry,” he said, bumping a knuckle against Izuku’s cheek. He picked up his phone.
How is he? Came a message in the class group chat. Katsuki sent a picture of Izuku and turned his phone off as the “awws” and “look at how cute he is” began to roll in.
Idiots, all of them. He’d probably have to barricade his dorm to keep them from barging in to steal Izuku from him.
“Always gotta make trouble,” he repeated, watching as Izuku climbed back up onto his pillow. He laid next to him for a few more minutes before sighing and rolling to his feet. Just because he’d been excused from classes didn’t mean he could slack on his homework.
Izuku watched him from the bed as Katsuki flipped open his books. His desk wasn’t more than a few steps from his bed, but to Izuku it must have seemed impossibly far. As Katsuki set to work he inched closer and closer to the edge of the mattress. Katsuki watched him out of the corner of his eye as he wandered around and bounced from spot to spot. He meant to keep a closer eye on him, but very quickly he got so absorbed in his work he stopped paying attention until there was a hard thump and he jolted up, a bolt of fear going through him, only to see Izuku standing with his hands on his hips, Katsuki’s phone on the floor in front of him. Izuku held his arms out expectantly.
“Needy,” Katsuki chided, smothering a laugh. He picked Izuku up and put him on his desk. When Izuku turned his back to him to look at the scattered knickknacks and scraps of paper, Katsuki poked him in the ass with his pencil. Izuku leapt up, hands flying, and whirled around to glare at Katsuki as he ducked his head to hide his laugh. He shook his head.
“Sorry,” Katsuki said, not sorry at all. Izuku turned around again, clearly ignoring him as punishment for being mean. It was just kind of funny given how little he was, and Katsuki was tempted to poke him again, if only to see his whole body move with it. A breeze could have blown him over right now. All the usual strength it took to bounce him around and now…
Katsuki looked between the pencil and Izuku, an idea forming in his mind. He licked his lips. There was no way Izuku would let him, right? He shouldn’t even think about it. He should finish his homework and see if he wanted more food, or, fuck, he didn’t know, something. He should be a good, responsible boyfriend, one who didn’t have those kinds of thoughts.
He made it another twenty minutes before he gave up. If he couldn’t get this stupid idea out of his head, couldn’t stop the image from writhing behind his eyelids, maybe he could distract himself. Redirect it or whatever, find a new way to spin it. That’s what he’d been advised to do about his nightmares, and yeah, okay, he hadn’t had the greatest success with that, but if all he could think about was his stupid, tiny boyfriend, he might as well mess with his stupid, tiny boyfriend, right? It probably worked better when he was actually in the situation instead of just freaking out.
He snapped his notebook shut and fixed his gaze on Izuku. Izuku startled, springing out from behind the action figure he had been examining. When he saw Katsuki staring at him his head cocked curiously. Katsuki held his hand out, palm up, and Izuku climbed in immediately.
Don’t think about it, Katsuki reminded himself, picking up his pencil. Izuku was looking up at him, wide-eyed and trusting. He stiffened almost imperceptibly as Katsuki brought the eraser end to his stomach, a slower, more intentional motion than his earlier prodding. Katsuki waited for him to squirm away or shove the pencil aside, but Izuku’s tiny hands flexed at his sides and he squinted in that way he always did when Katsuki was messing with him and he couldn’t figure out why yet. He was smaller, sure, but some things didn’t change, and Katsuki could read him like an open book. He knew every face, every motion, every thought Izuku had.
Okay then.
He slipped the eraser under the bottom of his shirt, pushing it up just enough to touch cold rubber to soft skin. Izuku jumped but didn’t move, so Katsuki kept going, hiking the shirt up until it was under his chin and his muscular chest was bared. Izuku let him, completely still, gaze fixed on Katsuki’s face.
Yeah, Katsuki was thinking about it.
“Would you let me?” His voice was softer than it had ever been. Izuku didn’t answer.
How far would he let Katsuki go?
Katsuki flipped the pencil around in his grip, pinching Izuku’s shirt between his fingertips. He tugged up once, not even really sure what he wanted, but if he knew Izuku, Izuku knew him, and he ever so obedient pulled his shirt off, the fabric barely a scrap as it fell slowly to the desk. Katsuki ran the sharpened end of pencil over his collarbone and down his chest, watching as it rose and fell rapidly, as the muscles of his stomach tightened as it scratched a steady line straight to his waistband. He barely had to slip the point into one of his belt loops before Izuku was scrambling to pull his pants off too, then his underwear.
Katsuki’s mouth was dry. He swallowed thickly, fingers tight around the pencil. Izuku was ten centimeters tall and naked in his hand. He was looking up at Katsuki and Katsuki was looking down at him, and fuck.
Fuck, he was so little.
“Would you let me?” He didn’t know if Izuku knew what he was saying, if he could understand the words as they left his lips, but he seemed to catch their meaning anyway. Maybe it was the desperation in his tone, the way he shifted in his seat, the way he held the pencil so tightly he thought it might snap. Maybe it was something on his face, the way he cupped Izuku, the way he had held him this whole time. Or maybe it was just that Izuku wanted it as bad as he did. Maybe Izuku had wanted it the whole time. Maybe he had crawled from All Might’s palm to Katsuki’s and felt it right then and there, had watched Katsuki’s fingers close around him, hand so big compared to him he could have held him down, pushed him around, picked him up, made him - made him -
Eyes still locked on Katsuki’s face, Izuku bit his lip and laid back, shoulders cradled in his fingers, body folded into his palm. His legs fell apart slowly, his little cock stirring between them as Katsuki traced the pencil over one thigh and then the other. He squirmed as the sharp tip circled inwards until it brushed against his balls, shifting his cock with it.
“Fuck.”
With a sudden intensity that startled Izuku so badly he nearly fell from his hand, Katsuki flung the pencil down and tore open every drawer he could reach until he found their lube, now hidden after one too many sleazy comments from Kaminari made Izuku’s ears turn red. Izuku wiggled, full-body shakes like he couldn’t do anything else, throwing himself onto his stomach and looking at Katsuki over his shoulder. Katsuki couldn’t string together a thought other than holy fucking shit as he fumbled with the cap. Finally he got it open, brandishing it above Izuku eagerly.
He was really gonna do this, wasn’t he? Izuku was really gonna let him.
He maybe should have put it on the pencil itself, but he wasn’t exactly thinking clearly here. He squeezed a little too hard, drenching Izuku nearly from head to toe, his whole body soaked, and man, somewhere along the way Katsuki had taken one too many hits to the head, because his wires had to have gotten crossed for that to make his cock pulse in his pants. He dumped the lube onto the desk. Fucking hell, he wanted to get his cock out so bad, but he just kept staring down at Izuku, wet and slippery and little little little.
With trembling fingers, he picked up the pencil.
He kept it clenched in his fist, pointer finger outstretched. He petted a finger down Izuku’s back and shook at how much of him it covered. Finger slick, he rubbed over his hole, not really pushing, just rocking, Izuku moving with him. He could feel it give slightly, feel Izuku stretch to take him like he always did, open and eager and loose and sloppy, well-fucked and well-used, and -
It occurred to him, almost hysterically, that he’d really like to watch Izuku fuck himself like this. His fingers would be too small to see, but Katsuki could picture his fist, wrist-deep and writhing, curled up in Katsuki’s hand, little mouth nipping at his fingertips like he was biting the pillow not to scream.
Later.
Later.
The pencil was smaller than his finger, but it still seemed enormous compared to Izuku. Katsuki followed the path down his spine with the eraser, watching Izuku’s thighs jump and shake as it dipped over the small of his back and over his ass. He ran it up and down, nudging his balls again, enthralled by the way Izuku pushed back against it with each pass over his hole. He could have sat there for hours, alternating between rough grinds and barely-there touches, but before long Izuku was batting at the pencil and scowling over his shoulder. Convinced he’d changed his mind, Katsuki started to pull away, but Izuku grabbed the shaft just below the eraser and dragged it back, lining it up with his hole. He tugged on it pointedly, and when Katsuki didn’t make any other move to deny him, let go and turned back around with a decisive nod.
Breath caught in his throat, Katsuki pushed.
Izuku squirmed as the eraser pressed into him. His fists balled in the crook of Katsuki’s knuckles. His head hung low, his breath the tiniest puff as it came rapid and heavy. Katsuki stared, unable to blink, as the eraser sank in, his hole stretched tight and pink around it. He ground down until the eraser was entirely inside him, half its fastener with it, and then he paused, waiting. Izuku was bowed so low his forehead rested on Katsuki’s finger. His arms were shaking. He didn’t move.
Katsuki dragged the pencil out until all that was left was the very tip, and then he pushed back in.
Izuku collapsed. His arms gave out from under him, from the strain or the lube coating both of them, ass still in the air. Katsuki groaned, twisting the pencil as he thrust it in and out, watching him rock with it, unable to do more than push back weakly, taking it further and further. Katsuki could picture his face, red and twisted and tearing up, already on the brink of sobbing, always overwhelmed so easily, so desperate to take what Katsuki would give him yet so helpless under what he already had. It must burn, he thought a little deliriously. The stretch must be unbearable, the intrusion so deep it ached, so deep it touched something in him Katsuki could never reach, but this was him, anyway. Izuku bucked and shook and he was surely crying, and Katsuki stared at the pencil as it pushed in, in, in, and fuck.
He honestly couldn’t have told you when Izuku came. Usually he prided himself on that, knowing when he’d tip over that edge and how far he could be pushed afterwards, but this time he was so enraptured, hypnotized by the roll of Izuku’s body as he was fucking violated. He didn’t notice he came, or honestly, if he even did, though he was sure of it, certain that half the shake was the overstimulation of one orgasm into another, pushed until his breaking point. What he did notice was when Izuku, now prone and lax and pliant, reached back with a trembling hand to fumble at the pencil again. Feeling greedy and cruel and dizzy, Katsuki fucked it in a few more times, and then he yanked it back out and threw it blindly to the floor.
Izuku looked blearily up at him as Katsuki shot to his feet. He fumbled at his belt and pants with one hand, clutching Izuku tightly. Yet again Izuku seemed to read his mind. Slowly he struggled onto his back, his whole body flushed and weak. A hand flopped across his stomach, the other at his side.
Katsuki freed his cock with a groan. With Izuku’s soft, sweet face burned behind his eyelids he jerked himself roughly, barely a few tugs before he was tumbling too. He held Izuku low, painting him in his spend. Izuku remained still and sleepy as he was drenched, a hazy smile on his face. Katsuki choked on a moan, stroking until he was sore. He slumped forward, all strength leaving him at once.
“Shit,” he rasped, throat dry. He looked down at Izuku. He couldn’t resist touching his cheek again, rubbing comfortingly. Izuku turned his head and nuzzled into it. Katsuki cracked a grin. “Needy,” he said affectionately. “Fucking hell.”
His legs were trembling when he stood up. He stumbled away from his desk, Izuku still cradled gently in his hands.
“You’re so -” There were a thousand things he wanted to say and no words for any of them. He leaned down, bringing his forehead to his fingers. “Thanks.”
In a few days they might have a way to fix this. Tomorrow Katsuki might wake up to Izuku back to himself, quirk worn off in his sleep. By dinner he might be laughing and swaying with Uraraka and the others, commiserating at what a strange experience it was to be so small.
But right now he fit in the palm of Katsuki’s hand, and Katsuki would take care of him.