Things even out as Katsuki gets more used to being friends—yes, he can actually think of them as friends. It becomes second nature to walk home to Izuku's apartment instead of his own. Things are easy while classmates are still exploring new quirks or just getting them. But Katsuki watches each day pass wondering when someone will label Izuku quirkless.
Katsuki turns four. His explosions are hardly puffs of smoke, a cheap magic trick in comparison to what he will be capable of someday. Izuku still looks at him with nothing but admiration.
Whispers in the classroom about Izuku's lack of quirk start three months after his fourth birthday. The teacher has talked about being quirkless, mentioned those rare cases that still exist. Katsuki's gaze finds its way to Izuku every time. He still hasn't given up hope. Not yet. The whispers in the classroom grow louder. A few people snicker when they see Izuku walk by. Katsuki glares each one down.
Maybe that's why no one drags Izuku out behind the school building just to laugh at him for being less than them. Maybe that's why Izuku doesn't have to suffer bullies. Because this time Katsuki isn't the bully. He stands at Izuku's side with a threat in his eyes that no one dares to test (even a puff of smoke is enough to make most preschoolers cry).
There comes a day when Izuku stops talking about when his quirk will manifest. His face is downcast, and the glow in his green eyes is a little less. Everything from the frown on his lips to the slope of his shoulders speaks of a sullen mood.
"I'm quirkless, Kacchan."
Katsuki's mouth opens.
But what can he say? He knows that Izuku will someday match him in strength. For now, for now, almost makes it past his lips, but he can't tell Izuku. He can't talk to Izuku about a past he will never know. Izuku endured a quirkless childhood once, without ever giving up hope.
After all, even if he's quirkless, he can—
"—still be a hero." He registers Izuku's look of open-eyed surprise before he realizes what he said. When the words make it to his own ears, he swallows uncomfortably, but doesn't take back the statement.
There's plenty you can do just being a nerd with a bunch of notes about heroes swimming in your head. There's plenty you can do without a flashy quirk. He has seen Izuku struggle, and he has seen him fight. A quirkless middle-schooler dashing forward when even pro-heroes wouldn't make a move.
Katsuki takes a breath. He's never been good at encouragement. Support has always been someone else's job, and for good reason, but he can manage this much.
"You'll never be a hero if you give up."
He meets Izuku's look of surprise. Katsuki is hardly one to give comforting words. He feels his face redden slightly. Fuck. Izuku looks at him for a moment, before his face relaxes into a smile that's already lost some of it's brightness. Being quirkless is hard. And it's only been two years since he was labelled thus. He has another eight years to go.
The next time Izuku asks him to come over—because he hasn't been able to get even a simple invitation to play video games or watch another damn hero documentary out in the two years he's been trying to be Izuku's friend—he says "let's have a sleepover!" Izuku's eyes light up with ideas of pillow forts and staying up past his usual bedtime. Katsuki says "yes" before he thinks about it—before he remembers he wakes up in cold sweat almost every night. He is in a nearly six year old body, and he carries memories of someone more than twice his current age. He says yes, and he can't take it back, not when Izuku looks at him with such a pure happiness on his face.
So Katsuki grits his teeth and decides that he'll try to stay up the whole night so he doesn't have nightmares he has to recover from. When he comes over to Izuku's apartment, it's like the other times. They play outside. But Izuku scrapes his knee, and Katsuki laughs at him until he sees tears form in Izuku's eyes and shit don't cry. He drags Izuku back inside and makes sure he puts a bandaid on it, even though it's barely bleeding. Then they play video games until Katsuki finally tires of kicking Izuku's ass in a racing game and beating his character to a pulp in another. Then Izuku's mother is there urging them to get some sleep.
They stand next to each other at the bathroom sink to brush their teeth. Katsuki accidentally elbows Izuku twice. The first time, all Izuku does is shift away slightly, but the second he steps away more dramatically.
"Kacchan, that tickles," he complains, voice muffled because of the toothbrush in his mouth.
There's a dribble of toothpaste at the corner of his mouth that irks Katsuki slightly, but he's more focused on something else. He spits into the sink and wipes his mouth on the nearest towel.
"You're ticklish?"
Izuku steps back. "No."
Katsuki eyes him for a moment before lunging. "You're ticklish aren't you, you fucking nerd? Deku, don't lie to me!"
Izuku doesn't react fast enough, and they end up on the tile floor. Izuku is most definitely ticklish, Katsuki learns. Very.
Inko pokes her head in to see what on earth all the squealing is about when all they were supposed to be doing is brushing their teeth. She opens the bathroom door to find Izuku curled up with tears of laughter in his eyes and Katsuki with a victorious smirk on his face. Her eyebrows raise in worry until Izuku sits up still holding back giggles.
"Don't do that," Izuku wheezes.
"No promises," Katsuki answers.
Inko sends them to bed after that. Katsuki is slightly astounded but not really surprised to find that Izuku owns no less than three sets of All Might pajamas. Izuku's room is also decked in various hero posters, most of which are also All Might.
They settle into Izuku's bed, which is easily big enough for two six year olds. Izuku falls asleep quickly, but Katsuki keeps his eyes open and stares at the ceiling. If he stays awake, he won't have nightmares.