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Izuku thought he knew everything about Katsuki already.
Or at least he thought so.
Until they started living together.
Even though he had known him since they were kids — He was even there the day his quirk first sparked, a tiny flash in his palm, a grin splitting his face— there was always things to discover.
Katsuki had been the first page of his hero analysis notebook. And probably the one with the most annotations and side scribbles.
And then they moved in together.
And Izuku started adding facts here and there. Until he has a full on Kacchan notebook.
Like how Katsuki was a morning person. Full workout, shower, breakfast — done by 7 a.m. sharp.
Meanwhile, Izuku would still be bargaining with his fourth alarm, curled under the sheets and pretending the sun didn’t exist.
He was also terrible at staying up late. They’d put on a movie at nine and Katsuki would be out by 9:30, without fail. It was worse at events or meetings — by 7 p.m. he’d be on his sixth cup of coffee, eyelids twitching but determined not to crash.
He liked cooking. That, Izuku knew.
But Katsuki really liked cooking. Like, if he hadn’t been a pro hero, he would’ve absolutely opened a restaurant and terrorized the industry with his standards.
He refused to eat in agency cafeterias. Said if the food tasted like crap, he’d rather go hungry and get his protein intake later. There was no need to suffer and eat bad food on purpose.
He was very, very organized.
And it wasn’t like Izuku was messy. He cleaned, he folded, he did his part. But if a laundry pile leaned a bit too far to one side, Katsuki would stare at it like it had committed war crimes.
And then… things happened.
They were in a relationship.
Probably .
They never sat down to have the talk, but it happened. It settled in. Everyone kind of rolled with it. Even them.
Which meant Izuku had to start a new Katsuki section in his Kacchan notebook.
And the first entry?
Kacchan was surprisingly very touchy.
Izuku wouldn’t have believed it — not in a million years — if he hadn’t been on the receiving end of it.
For the third summer in a row, their request to install an air conditioner had been denied. Being top-ranking heroes apparently didn’t mean anything to the property management company.
Granted, Katsuki had threatened to blow the building up when they first applied for the lease, so… they weren’t exactly fans.
So summer nights meant sleeping with a fan, minimal sheets, and absolutely no unnecessary touching. Or else they’d both melt.
Izuku had just gotten out of the shower, towel still half on his head sitting flat on his stomach on the bed, dangling his feet.
He was scrolling through news on his phone, the whirring fan nearby doing its best. Katsuki, like clockwork, had dried off, tossed the towels in the hamper, and knocked out by 10 p.m. like a grandpa.
The bed creaked.
Izuku glanced up from his screen to find Katsuki shifting. His brows were furrowed, one hand patting blindly at the mattress like he was searching for something.
Then Katsuki cracked one eye open, sleep-blurred and dazed, and turned his head in Izuku’s direction.
Izuku smiled softly, setting his phone aside.
“Did something wake you, Kacchan?” he whispered. “The lights? I’ll turn them off in a sec.”
Katsuki reached with his hand and ruffled his hair half-heartedly. It was more like sleepy patting and hand flopping against his head.
“Whatchu still doing up?”
“Checking the news,” he said, turning off the light. The room dimmed into a warm hush. “I’ll sleep.”
He rolled over to face him. Katsuki’s eyes were closed again, mouth slightly open.
So peaceful. So handsome.
Then—
“Why’re you looking at me?” he mumbled.
Izuku smiled. “No reason. You’re just very handsome.”
He closed his eyes too, snuggling into the pillow. “Goodnight, Kacchan. I love you.”
Katsuki rarely said it back.
But that was okay. He didn’t need to. He showed it in other ways.
“Go to sleep, you stupid nerd.”
A low grumble.
Then—
“Hand.”
Izuku peeked one eye open. “Hand?”
Katsuki, barely conscious, reached over and grabbed Izuku’s hand with his own, pressing it under his cheek like a pillow.
His grip was firm.
Possessive, even.
“Hand,” he mumbled again, already halfway back to sleep.
Izuku lay there, hand trapped beneath Katsuki’s cheek and fingers, his own face flushed and heart bubbling.
He stared at him, smile stretching quietly on his lips.
Yeah .
Kacchan was… very cuddly.
Izuku wasn’t much of a cook. In fact, Katsuki had banned him from half the appliances for safety reasons.
But this time, he stood in front of the stove, stubbornly determined.
Katsuki shuffled into the kitchen, shirt half-on, rubbing his eyes.
“What are you burning?” he mumbled.
“I’m not burning anything,” Izuku said, standing protectively in front of the pan. “It’s just an omelette.”
Katsuki leaned over his shoulder, placing one hand firmly on his waist. The heat of his palm pressed through the fabric.
“The one thing I know I can’t mess up,” Izuku added, hopeful.
Katsuki peered over his shoulder. His hand stayed where it was, fingers splayed, squeezing the tender skin. “Your technique is shit ,” he said calmly.
Izuku smiled, not moving. “I’m trying .”
“You’re gonna overcook it.”
“Then help.”
“I am helping.” His hand gave a slight squeeze. “I’m here.”
And he stayed like that, pressed behind him, inspecting the omelette like it was a threat to national security, his other hand eventually joining the first. Wrapped snug around Izuku’s waist.
Katsuki just… needed a hand on him whenever he was around.
Izuku didn’t mind.
During the latest Class A reunion, things were as loud and chaotic as ever.
Katsuki wasn’t much for PDA. Never had been.
The whole class knew about them — though some were more oblivious than others. Shouto, for one, still asked how they were so touchy for roommates.
They always sat next to each other.
And Katsuki, mid-conversation with Eijirou, would just casually rest a hand on Izuku’s thigh under the table.
Didn’t say anything. Didn’t do anything.
Just there.
Firm and warm and grounding.
Izuku would glance at him.
Smile.
No one noticed. Probably.
Later that night, Izuku opened his notebook.
He jotted something down under a new heading.
Kacchan is very touchy.
He stared at it for a second.
Then underlined it once.
And added a small, lopsided heart next to it.
Just because.
Then, under it, he scribbled another line.
Kacchan is very caring.
That one, he underlined twice.
He tapped the page with his pen, remembering.
It had been a long day. The kind of day where his limbs ached down to the bone.
The kind of pain that settled in quiet — leftover scars, old wounds, reminders from the war.
Izuku sat on the bed, legs stretched out, the dull light of their night lamp casting a sleepy hue across the room. He was half in his pajamas, half not.
He reached for the thick jar of cream Katsuki had bullied him into buying months ago. Something about nerve damage and proper scar hydration.
He dipped his fingers in and started rubbing at the ridges of his left knee, careful and slow.
There was a rustle as Katsuki walked in from the bathroom, drying his hands on the hem of his shirt.
He said nothing for a beat, just stood there at the foot of the bed, watching.
Then he walked up. Quiet.
Took the jar out of Izuku’s hands without a word and sat beside him.
“I can do it alone, you know,” Izuku mumbled, not meeting his eyes.
“I know you can,” Katsuki said, dipping his fingers into the cream. “But I can do it for you too.”
He started with Izuku’s ankle, working slow circles, warm hands steady and gentle in a way no one else ever was.
Like he knew exactly how much pressure to apply.
Like he knew exactly where it hurt.
Izuku sat there, blinking fast.
His throat felt warm.
Katsuki didn’t say anything else.
He didn’t need to.
Later that week, Izuku was hunched over the kitchen table, papers everywhere, laptop open to three tabs, and a half-empty tea mug growing cold beside him.
He was working on his class schedule, lips moving without sound, already spiraling.
“I need someone to help me with this,” he muttered, fingers tapping the table. “Can’t do all twenty-five of them alone…”
Katsuki walked in with a fresh cup of tea, nudged aside the cold one, and placed the warm mug near his elbow.
“Whatchu doing?”
Izuku sighed. “Trying to figure out who I can ask to co-host the next practice exam. It’s too much alone.”
Katsuki didn’t even hesitate. “Sure. I’ll come.”
Izuku blinked. “You will? But… I didn’t want to impose. You always guest lecture for me. I thought you’d be tired.”
Katsuki leaned in, kissed him softly.
A simple peck.
A tender kiss.
“ Please impose, stupid nerd.”
Then he turned and left the room, already sipping his own tea like it was nothing.
Izuku blinked once.
Twice.
Then smiled.
Turned back to his laptop. And wrote Katsuki next to the slot.
They were walking down the corridor of the Musutafu Police Station, just finished filing their witness statements, still in partial gear.
Izuku’s phone pinged.
He opened the message, frowned.
“Ah, shit…”
“Uhum?” Katsuki grunted beside him, not looking up.
“I need to drop my mom off at the airport next week but it’s at the same time as my gear revision…”
Izuku started muttering. “Can’t say no to her, obviously. She’s going on that trip with the ladies from her Pilates class. They all became besties. And I really don’t want her to go alone. She has a heavy suitcase, but I can’t move the revision, they already booked the tech support…”
Katsuki stopped walking.
Turned toward him.
Grabbed him gently by the top of the head and tilted his face up.
He leaned in, deadpanning.
“Yeah, I wonder what you can do, you useless nerd with no driving license who happens to have someone with a car and a license standing right here.”
Izuku blinked. “Erm… You wanna drive my mom to the airport?”
“If it helps,” Katsuki shrugged.
“I don’t wanna bother you…”
Katsuki closed his eyes and sighed so hard he ran out of air.
Then, he grabbed Izuku’s wrist and dragged him into the nearest broom closet.
He pressed him against the wall, both arms coming up to cage him in.
Hard stare.
“Learn to lean on me, Izuku.”
Izuku’s eyes darted. “I just… I don’t want to bother people.”
“I ain’t people ,” Katsuki growled, grabbing him by the chin. “I’m Kacchan . Okay? Get that in that stupid head of yours.”
He gave his forehead a knock, leaned in, and kissed him — a firm peck.
Then he shoved his hands in his pockets and left the closet like nothing happened.
Izuku stood there.
Touching his lips.
A little breathless.
Kacchan called himself Kacchan.
And Kacchan was… so caring.
Satisfied with the new added line, Izuku smiled at the words, thumb tapping the edge of the notebook.
Kacchan is very touchy.
Kacchan is very caring.
He turned the page, waiting.
Then came the next entry.
Kacchan is really spoiling me.
He grinned.
And yeah, that one had a story too.
He arrived at the same time as the delivery woman.
“Delivery for one Midoriya Izuku?” she asked, clipboard in hand.
“Oh, that’s me! One second, please,” Izuku chirped, fumbling through his bag for the little seal stamp. “Sorry— sorry, I always forget which pocket I put it in.”
The woman smiled politely, waited.
He finally pressed his seal onto the tablet and accepted the long rectangular package. It was heavier than expected.
“Thank you!” he said, holding it awkwardly under one arm.
He didn't remember ordering anything.
Once home, he kicked off his shoes, set the box on the dining table, and started peeling off the layers of tape.
It was industrial packing — something Hero-related, probably. His brows pinched in curiosity.
And then, just as he got to the last flap and pulled the lid open — revealing a shiny, polished, unmistakably new pair of gauntlets — he heard the door open behind him.
“Sup’...” came Katsuki’s voice, casual and gruff as always, as he threw his keys on the entrance cabinet and toed off his shoes. “Ugh, my calves are killing me.”
Izuku blinked at the gauntlets in his hands. “Kacchan… what are these?”
Katsuki glanced over, already tugging off his utility belt. “Oh. Your gauntlets were startin’ to get fucked. Ordered new ones. You should check with tech to adjust ’em to your gear.”
He then disappeared into the bathroom.
“You— yeah, but—” Izuku stammered, lifting them as if to prove a point, “why did you buy them?”
Katsuki’s head popped back into view from the bathroom, bare torso on display. He raised an eyebrow.
“I said —because yours were fucked. You got hearing problems?”
“Kacchan!” Izuku gasped, scandalized. “You can’t just keep buying me stuff! You already got me my gear!”
“Correction,” Katsuki grunted, turning back into the bathroom, “the whole class got that one.”
“Stop lying. I know it was mainly you. You lived off cup noodles for five years to get it.”
“Well I ain’t living off cup noodles to get gauntlets now,” Katsuki called from inside. “Also—I beat you in the charts this month, by the way.”
“I don’t care about that,” Izuku muttered, already walking after him.
Katsuki had turned on the shower, steam starting to curl out from under the door.
He had his pants halfway down his thighs, not caring in the slightest that Izuku was there.
Izuku, for his part, paused. Just for a second.
Katsuki was... really attractive.
It was almost unfair, honestly.
He had a lean, muscular frame, body honed and sharp in all the right places, scarred in the most beautiful ways. The kind of body that made Izuku feel things just looking at it.
He swallowed hard as Katsuki got into the shower.
“You need to stop buying me overpriced stuff,” he said instead, cheeks already red.
Katsuki opened the shower door halfway, stepped out slightly, and reached for Izuku’s chin. He pulled him in close until their noses nearly brushed.
“Who am I?”
Izuku blinked. “Katsuki?”
“Nope.”
“…Kacchan?”
“ Right . And what do you do when Kacchan buys you shit?”
Izuku sighed. “I take it and shut the fuck up?”
“ Yeah . Now enough talk,” Katsuki mumbled, already working on the buttons of Izuku’s shirt.
“Kacchan? What are you—”
“Less talkin’, more takin’ off clothes.”
Izuku stood there, watching him fumble with the fabric.
A soft chuckle left his lips as he reached to ease his pants off, fumbling with the belt and letting them drop.
Katsuki tugged the shirt off, threw it somewhere vaguely toward the laundry basket, and smirked.
“Now this is what I’m talkin’ about.”
He grabbed Izuku by the back of the neck, pulling him into the shower, steam engulfing them instantly.
The water was hot, and their skin slickened quickly, chests pressed together, hands skimming over damp skin like a second exploration.
Katsuki’s hand gripped his waist, firm and grounding, the other cradling the back of his neck.
“How was your day, Kacchan?” Izuku asked, breath light, lips brushing along the line of his jaw.
Katsuki tilted his head down, lips brushing just above his.
“It just got better now.”
He said it in a murmur. Like a secret.
Then he kissed him.
And the rest… well.
The rest was all about giving and receiving.
Later, when Katsuki had conked out early again—snoring softly with a hand on Izuku’s thigh, of course— Izuku slipped out of bed and grabbed his notebook.
Kacchan is very touchy.
Kacchan is very caring.
Kacchan is really spoiling me.
He smiled. And then scribbled down a new entry.
Kacchan always takes care of me. Even when I’m being stupid.
The Class A reunion had gotten loud, fast.
Drinks were flowing, laughter bouncing off the old walls, and someone had started a karaoke queue nobody admitted to filling.
And Izuku?
Absolutely, thoroughly, shamelessly hammered.
“Imma get this stupid moron home,” Katsuki grunted, catching Izuku by the collar as he nearly tripped over Mina’s feet.
“Good luck!” Kaminari called after them.
As the door closed behind them, Tsuyu leaned into Ochako. “I wonder what Izuku sees in him.”
Ochako tilted her head. “Maybe he has sides we don’t see.”
“We know him well. Of course he has good sides,” Tsuyu said plainly. “But why stay with someone who calls you stupid all the time? Who swears at you like it’s punctuation?”
Ochako just shrugged.
The heart wanted what it wanted or something.
Izuku puked twice on the way home.
Tried to fistfight a streetlamp “you smug bastard” he said, and obviously lost.
Missed a curb and fell flat on his face.
Once they got through the door, Katsuki stripped him like a muscle memory—jacket off, shirt over the head, belt undone. Threw him into the shower, stuck a toothbrush in his hand, shoved a water bottle in his mouth.
In fifteen minutes, Izuku was clean, hydrated, and in underpants, starfished on the bed.
“Kaaaacchaaaaaan,” Izuku whined as Katsuki started pulling off his own shirt.
“Tone it down or I’ll knock you out with a pillow, dumbass.”
“ Kaaaacchaaaaan ,” Izuku repeated, in a whisper this time which was equally loud, a grin twitching at his lips.
Katsuki huffed a laugh, finally crawling into bed beside him, bare chest glinting in the soft streetlight outside the window.
His head rested on his hand, elbow on the mattress. “What is it now?”
“I love you,” Izuku mumbled, eyes half-lidded, voice soft and stupidly sincere.
Katsuki blinked, then leaned in, brushing his mouth against Izuku’s in a slow and lingering kiss.
“I love you too,” he whispered, just barely.
Izuku blinked up at the ceiling. “ Woooow . I should record this historical moment.”
Katsuki snorted and flopped onto his back with a sigh. “I say it back all the time.”
Izuku blinked, then turned his head. “More like once for every fifty times I do.”
“That’s ‘cause you say it ten times a damn day.”
Izuku didn’t respond.
Instead, he rolled over—splayed full-length across Katsuki’s whole body, limbs tangled without shame, cheek squished flat against warm skin. The feeling of skin on skin grounded him instantly.
He let out a soft breath.
“We never know. You might forget that I do. And then…I don’t know, go take care of a less stupid, less nerdy guy.”
Katsuki looked down at him, eyes half-lidded. “You're a dumbass.”
Izuku smiled, lifting his head lazily.
Then, with both hands, he grabbed Katsuki’s chest and gave a firm squeeze.
“I fucking love your man boobs, Kacchan.”
Katsuki raised an eyebrow. “They’re pecs.”
“When they’re this size? They are boobs .”
“They’re not—” Katsuki groaned, giving up on this debate. “You’re swearing now? Yeah, you’re definitely drunk.”
“I don’t need to be drunk to appreciate a good chest.”
“Oh, so it’s a chest now?”
“Slip of the tongue. I’m drunk.” he said, then leaned in and licked over one nipple, quickly but deliberately . “They’re boobs.”
Katsuki froze . “Izuku…” He said in a warning tone.
But he didn’t stop.
He flicked his tongue, then dragged his lips to the other one, giving it a soft bite.
Katsuki’s breath caught.
“You like it when I lick them,” Izuku said with a smirk, biting his lip, drunk but still smug.
“Not when you’re one jolt away from puking on them.”
Izuku pulled back with a scandalized look. “ Ew . Kacchan, you have weird kinks.”
Katsuki gave him a look.“It was hard a second ago. This puking imagery calmed me down. Thanks.”
Izuku snorted and buried his face against his chest again. “Uhum… good night, Kacchan.”
“Sleep, stupid nerd,” Katsuki muttered, running his fingers through his curls until he passed out on top of him.
Izuku woke up groggy.
He sat up slowly, groaning.
His head hurt.
His throat hurt.
His pride hurt a little too.
He stretched, rubbed at his eyes—and spotted Katsuki leaning against the doorframe, arms crossed, looking far too smug for this hour.
“Good morning, drunkard.”
Izuku groaned. “Morning, Kacchan… Thanks for taking care of me last night.”
Katsuki's grin widened. “Oh, you’re so welcome.”
Then he walked forward and—without warning—grabbed both his ankles and dragged him down the bed in one fluid motion.
“Kacchan?!” Izuku yelped.
Katsuki settled between his legs, eyes dark.
“Now that you’re up and sober,” he said, voice low, “I’m gonna show you what an enraged dog looks like.”
“ Kacchan ,” Izuku said with a breathless laugh, chest rising. He remembered last night. “Wait—don’t tell me you're still mad about the boobs comment—”
Katsuki dipped his head into the crook of his neck, teeth grazing the skin.
Slowly, he let his hand slide into his underwear. “Say it again. See what happens.”
Izuku chuckled, flushed with sudden warmth.
“You do have sensitive boobs , Kacchan.”
Then the hand that had been working inside his boxers gave a firm squeeze. “And you have a sensitive co— Agh… ”
With eyes glinting with mischief, Izuku reached up and gave one nipple a gentle flick.
Katsuki froze . His hand stopped.
He looked up with murder in his eyes.
“I am going to fucking ruin you.”
Izuku just grinned. “That’s the goal.”
Katsuki growled—and then pounced .
Later, they stood quietly on the balcony, watching the city hum below them, golden hour setting the rooftops ablaze.
Neither spoke for a long time.
Then Izuku turned, gaze soft. “I love you.”
Katsuki gave him a sideways look. “ Whatever , you fuckin’ sap.”
But he reached out.
Ruffled Izuku’s hair like it was instinct.
Izuku just smiled.
People often asked him what he saw in Katsuki.
But they didn’t see how his ears turned slightly red when Izuku said I love you then threw a snarky comment out of embarrassment.
They didn’t know he was playful, thoughtful, and loyal beyond any logic.
They didn’t see how he always knew what Izuku needed before he said a word.
They didn’t have a Katsuki notebook.
And honestly?
Izuku was glad.
He didn’t want anyone else to know about this Kacchan.
The playful, horny, funny, caring, loving Kacchan.
This one was his Kacchan.