At six years old it's difficult to stay awake for an entire night. At six years old, he finds his eyes heavy with fatigue before the clock on Izuku's bedside table reads midnight. At six years old, it's impossible to keep the nightmares away.
They come like they always do—shadows seeping into happier dreams. He dreams of simple things first. He dreams of beating up villains or standing on top of the world with a crowd cheering for him. Other times he dreams of a future in the other world—a future where he sits beside the Izuku he'd been so cruel to for so long. A future where they sit shoulder-to-shoulder. (A future where he had a chance to ask for forgiveness. A future where it was given).
The nightmares roll in like black fog, obscuring whatever he was seeing before and engulfing his consciousness. They aren't always clear. Aren't always full memories. But there are always screams. It is always dark. He can see vague outlines and shadowy shapes. He can feel the blood dripping down his skin.
In a mass of screaming voices, Izuku's is the clearest, its tone piercing through the darkness like a knife. Katsuki never makes it in time. His steps are moment late, a little too slow, and his hand falls short, fingertips grasping for something out of reach.
Someone calls his name in a small voice. The nightmare releases him slowly, tendrils of darkness and fear still clinging to his thoughts. Katsuki rises through layers of consciousness, until he feels hands gripping his shoulders and shaking him. He hears Izuku's voice—younger, not screaming in agony.
"Kacchan, Kacchan!" Izuku's voice is desperate (a little too reminiscent of those nightmares).
"I'm awake dammit," Katsuki answers. His throat is dry, and Izuku, no doubt, hears the unsteadiness in his tone.
"Kacchan, are you okay?"
Izuku fixes him with a concerned look in the soft glow the night light provides. He wonders how many times Izuku has asked that question and how many times he brushed it off as a nuisance.
Katsuki pushes himself into a sitting position with shaking hands. His body feels weak, and his heart feels like it's beating out of time. Cold fear lingers in the back of his mind. He has to remind himself that Izuku is there with him. Right there. Close enough to touch.
"Yeah, I'm fine." There is a tremor in his voice as he speaks, and he knows Izuku won't believe him for a second. All he hopes is that Izuku won't ask about the nightmares.
Mercifully, Izuku stays silent. He does, however, hold out one hand, his fingers spread open. "Whenever I have a nightmare, mom does this," he says.
Katsuki sees the determined look in his eyes and stares at his hand. (It's not scarred. Not even calloused). Katsuki remains frozen still.
"Take it." Izuku wiggles his fingers.
Izuku looks at him expectantly. His eyes are bright green even in the low light of the room. Katsuki glares back petulantly. Holding hands is stupid, and his quirk—but Izuku looks at him without fear. It's concern he sees reflected in Izuku's eyes. And trust. Katsuki relents. Lets Izuku take his hand and intertwine their fingers. They lie back down facing each other. Izuku gives him a ridiculously happy smile.
"It's ok," Izuku tells him. "There's nothing to worry about."
"Shut up, shitnerd. Just go to sleep."
Katsuki sleeps the rest of the night without nightmares. His dreams are peaceful for once.
They wake with the sun in their faces from the window with a curtain that they forgot to close. Their eyes open at the same time, eyelids fluttering in an attempt to clear the sleep away. Katsuki lets go of Izuku's hand like it burned him. But even after he pulls away, his palm remembers the shape of Izuku's hand.
Izuku asks him if he slept well, and asks about the nightmares too. Katsuki gives noncommittal answers to both questions.
It's the conclusion to the first of many times Izuku asks him to sleepover. They stay up later as they get older, playing video games or talking about heroes or whatnot. Katsuki tries to stay awake to avoid the nightmares. Izuku grabs one of his hands every time. Then they wake in the morning at the same time. It's a good routine. Comfortable.
Katsuki tries not to take it for granted that Izuku will always reach for him. Izuku never asks him what the nightmares are about after the first time.
As he grows older, the nightmares stay the same. As he grows older, he starts reaching for Izuku's hand first.