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Kirishima is a cat.
It is the only explanation Izuku can come up with which makes any sense at all. The cats around his neighbourhood used to fight to be in the best resting places, and they would roll and move to stay in a sunbeam travelling across the garden. Kirishima is the same, it seems.
The second they have free time and the sun is out, Kirishima is finding the very best bit of light he can and spreading out in it at as much as possible.
And, inexplicably, he's started taking his shirt off to do it.
The first time it goes sort of unnoticed, except by Izuku who notices everything – thank you very much. They finish physical training, and it is hot and humid as they all walk back towards the locker rooms. Kirishima strips off the upper half of his training uniform, tying the sleeves around his hips before running a hand through his hair, dislodging his sweat band.
When he stops before the shadow of the building – into which the rest of the class 1A are hurrying in an attempt to escape the heat – Izuku half turns to watch. Kirishima has his eyes closed with his arms spread wide, an expression of utter contentment on his face. And then Katsuki barks at him.
“Hurry the fuck up, Shitty Hair! I'm not waiting for you to spend half an hour fixing your spikes again. Move it.”
Kirishima's smile changes, ever so slightly, just a soft little uptick at the corner of his mouth. Izuku recognises it as Smile Number Four: the Katsuki smile. It's odd, because most people duck and cower when Katsuki growls at them like that, but Kirishima never has.
“Sorry Bakugo.” Kirishima turns his face up towards the sky again, inhaling like he's drinking in the sunshine, and then the moment breaks along with a passing cloud and they all head inside.
After that, Izuku notices the way Kirishima gets shirtless the moment the sun is out.
Between classes, jacket discarded and shirt hanging off his shoulder, even though fixing his tie again before class takes longer than the amount of time he spends in the sun.
When running, tee stuffed into the back of his sweats, jogging along happily, skin glistening.
When training, the upper half of his uniform burnt away, from when Katsuki explode-propelled him across the training grounds as a solid object to cause maximum impact damage.
At lunch, on the rooftop as he leans back against the railings, shooting the breeze with the rest of the bakusquad whilst Katsuki berates their lunch choices.
And no one says anything, and it’s certainly no business of Izuku’s. It makes sense, he supposes, because Kirishima’s Hero costume is low on fabric anyway, and any time he uses his Quirk in a meaningful way, he shreds his training uniforms. Kirishima is a confident guy, he’s plenty happy without a shirt in any given situation.
And he clearly loves being in the sun, his skin so much more tanned than anyone else in the class due to his habit of catching the rays whenever he can, even if it’s just for a few minutes.
Which is why Izuku doesn’t think much of it when Kirishima arrives in the common room, dressed in nothing but sweats with his hair tied back and a maths textbook under one arm. The common room is mostly empty – just Izuku sitting at the table with no less than six notebooks of different colours and a variety of shaded marker pens in order to highlight and organise his class notes and personal observational records – and apparently:
“Bakugo! Sorry bro, I didn’t see you there.”
Izuku glances up in time to see Katsuki’s arm stick out from behind the sofa and push Kirishima away roughly. The redhead just laughs, sharp teeth bright in the sunlight as he grins.
“You could look where you’re fucking going, Stupid Hair.”
“Sorry, sorry. I just… I wanted to sit in the sun.”
Kirishima’s pout should be illegal, Izuku decides quickly. No one who can smash through a wall with a single punch should be able to look like a kicked puppy so easily. From where he’s sitting, Izuku can only see the top of Katsuki’s blond spikes, but he watches intently over the top of his wall of notebooks and neon-rainbow stationary, as the other boy looks up at Kirishima. Kirishima tilts his head, lower lip pulled in between his teeth.
And then the unimaginable happens.
Katsuki gets up, grabbing his own notes and text books, and without looking over his shoulder, moves to the other end of the sofa, out of the sun. It takes less than a second for Kirishima to slink into the space, shuffling and settling himself until he is both perfectly comfortable and maximumly exposed to the warm light, but Izuku is still staring at the back of Katsuki’s head.
At best, he expected Kirishima to have had to sit somewhere else and sulk, and then probably get snapped at for sulking. But as Izuku stares – his own notes forgotten – the back of Katsuki’s head moves again, there is a creek of the sofa, and then Katsuki’s blond spikes and the stray red strands of Kirishima’s red ponytail are brushing together as Katsuki leans close to the other boy.
“No, you’ve got that wrong.” Katsuki’s voice is soft and low, and almost nothing like Izuku is used to hearing it. Not in years, and certainly not in company. “You divide by three here…”
There the scratching of a pencil, then:
“You’re gonna have to start again, Ei.”
“Oh.”
“I’ll help you.”
Izuku blinks. Katsuki called Kirishima by his first name. By a diminutive, familiar version of his first name. Izuku isn’t sure he’s ever heard Katsuki use anyone’s first name before. Izuku knows he’s going to need to make notes.
“Thanks, Bakugo.” Kirishima murmurs.
Izuku keeps his head down and works, but when the others from Class-1A roll in with drinks, snacks, and plans for a movie, he doesn’t miss the way Katsuki kicks quickly to the other side of the sofa. In the orange notebook Izuku keeps for these things, he makes a single last remark.
Kirishima sounded very much like he wanted to call Kacchan something other than ‘Bakugo’.
*
No one can prove that Kirishima has moved the furniture in the common room, because no one saw him do it, but Izuku is pretty certain that couch didn’t used to be there, and that the three easy chairs weren’t so close to the television before. It doesn’t matter, as such, but it does mean Izuku will need to update his floor plan in the pale green notebook he uses for general observations on dorm life.
The couch is now right in the centre in the big square of sun falling through the south window.
Ashido, Hagakure, and Asui are playing cards. Kaminari’s character is trying to defend his flag on screen from the entire team Mezo is playing as with every controller they own. Sato is baking something whilst Aoyama and Sero ‘help’. But what is observable by everyone, is that Kirishima is sprawled across the entire sofa by himself, shirtless, and looking blissfully sleepy in the hot afternoon sunshine.
For a very small moment, Izuku is jealous of his classmate’s ability to just lie around and snooze without caring who sees him or what they think. And then Katsuki pushes roughly past him, slightly damp black tank and loose shorts evidence that he has been out for an extra jog.
Because of course, Katsuki has pushed himself to run an extra three miles around the campus. It’s the kind of thing which only makes sense to Katsuki.
Katsuki stalks over to the couch and glares down at the shape of Kirishima napping.
“Move it, Shitty Hair.”
Kirishima rumbles sleepily, rubbing his cheek into a cushion. Katsuki kicks the sofa sharply, and Kirishima cracks open one red eye with a soft frown forming between his brows.
“You’re standing in the sun,” Kirishima grumbles. He wriggles, half rolling to put a bare foot on the floor, as though he can scoot the sofa out of Katsuki’s shadow without actually getting up.
Katsuki spends a moment looking down at his friend, expression inscrutable even to Izuku who has spent most of his life learning all of the little tics which give away Katsuki’s moods, and then he sneers and jabs his toe into Kirishima’s bare calf.
“Up, up!”
Kirishima whines – actually, legitimately whines – and Izuku braces himself for the collateral damage of one of Katsuki’s smaller explosions. But just as he is pulling an arm up to shield his eyes, Izuku sees Kirishima haul himself into a sitting position, looking decidedly pouty.
No person has ever produced such a heart wrenching reaction to being told they cannot lie in the sun any longer. He looks close to tears.
Katsuki rolls his eyes.
“You’re such a loser.” Katsuki turns and sits in the newly vacated space, curling one leg up before pulling Kirishima bodily across him, until the red-haired boy is lying back the beam of sunlight, head pillowed on Katsuki’s chest.
Izuku is sure he does not imagine the way Kirishima nuzzles into Katsuki’s t-shirt. Katsuki is a hundred and fifty pounds of post-run sweaty teenage boy. Objectively pressing one’s face into that is disgusting, but Kirishima is… smiling. Beaming really, just as bright as the sunshine he is basking in.
“See, now you still have the sun.” Katsuki uses one hand to ruffle then smooth Kirishima's floppy end-of-the-day spikes. “Fool.”
Izuku is very aware of the fact that other people have paused to observe the phenomenon of Kirishima not dying and Katsuki being… accommodating? The very idea sits weirdly in Izuku’s mind. Katsuki hasn’t willingly given way to the desires of another person in years. But there is Kirishima, sprawled out in the sun and melting happily beneath the continued stroking motion of Katsuki’s hands.
Izuku only hears what he says next because observing people closely has gifted him with excellent lip-reading skills.
“Will you braid my hair?”
“Shut up, Ei.”
A pause, Katsuki tilts his head microscopically.
“Maybe later.”