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Killua’s always been a monster. Ever since a young age, he’s known his place—and that place tucked under someone’s bed, causing unease, instilling fear. His first memory is of someone screaming, of haunting dark spaces, feeling a smirk on his face as he brings terror to yet another human.
It’s what he’s made for. He’s built for the job; slitted eyes, furry skin, long claws, fanged teeth. He’s downright monstrous.
He never expected the day to come where that wouldn’t be enough to scare someone anymore.
Killua’s first night with his next target is the same as any other. He’s nestled underneath the bed, same as always. Gleefully, he thinks of what his first move will be. Perhaps he’ll growl when his new victim least expects it—maybe he’ll tug at the blanket in the dead of night.
The child and his mother enter the room.
A weight settles onto the bed above him.
“Goodnight Mito!”
The boy’s voice rings out, followed by a small giggle. There’s a faint lisp that coats the words.
“Goodnight. Try to rest up, okay? We have a big day tomorrow.”
Killua watches as a pair of feed pad out of the room. Now is the perfect time to make his first move; to strike when his target is walking the line between sleep and wakefulness.
Silently, he reaches a hand up to the mattress, feeling around for warmth, fingers searching—
—and finally touches flesh.
It’s a small gesture. Killua’s perfected it by now. A small enough gesture to create unease, to make humans question if something truly touched them or if they were just imagining things.
He hears a gasp.
Killua smirks.
Then, without a moment to breathe, the weight on the bed shifts. Oh—wait, where’s he—
A head pops into view, upside down, painted with a curious expression.
“Who are you?”
Killua blinks, flabbergasted.
“Uh…”
The boy’s wide brown eyes blink back.
“Was that you touching me just now?”
He searches for any sign of fear—a trembling lip, a welling of tears, skin going pale from shock. Something. Anything. But all he’s met with is the boy’s inquisitive stare, looking at him with nothing but pure interest. There’s no traces of terror, not even a little.
“...yes?” Killua chokes out.
The boy huffs.
“I’m trying to sleep, silly,” Gon frowns. “It’s not nice to touch people when they’re trying to sleep, ya know.”
“Aren’t you scared?” Killua asks, confused.
“Am I supposed to be?”
“I’m the monster under your bed, dummy. Of course you’re supposed to be scared,” he snaps, mouth pressing into a hard line.
“You don’t look very scary to me,” Gon replies. It’s so nonchalant, completely free of fear.
Killua’s not sure how to respond to that.
“What’s your name?”
“You find a monster under your bed and want to know my name?”
“Well, I have to call you something. You have one, don’t you?”
“Killua,” he huffs. “My name is Killua.”
“I’m Gon!” he giggles. “Please don’t tickle me anymore, Killua. I’m very sleepy.”
“Okay. I’ll try scaring you again tomorrow I guess.”
“Goodnight, Killua.”
“...good night.”
Gon smiles at him—wide and toothy—before swinging back up above, dipping from Killua’s line of sight.
Killua listens as the weight above him shifts once again.
Tomorrow. He’ll try again tomorrow. This time, he’ll scare Gon for sure.
———
Killua’s grown accustomed to their little nightly routine by now.
But Gon’s getting older—Killua is too. And with age comes young adulthood, which comes with… adult things.
The first few times he hears Gon touching himself he ignores it as best he can. He pretends not to hear the gasps and moans, to not hear the squeaking mattress above him, the final strangled sound that comes out of Gon’s mouth when he—
—Killua squeezes his eyes shut.
It’s not an easy task.
“Goodnight, Killua,” Gon says as he turns the lights off.
“G’night,” he replies. “I’ll try scaring you again tomorrow.”
“Sounds good. Keep it up. Maybe you’ll get lucky. Try grabbing me next time. I like when you touch me.”
“You’re not supposed to like it,” Killua grumbles.
Gon lets out a laugh before settling under his sheets.
There’s a long stretch of silence.
Maybe Gon’s gotten it out of his system by now.
As soon as Killua thinks they’re finally back to a quiet, normal night, he hears the sheets move. There’s a shuffle of fabric, followed by a shift of weight.
He watches as a pair of underwear lands in front of his line of sight.
That’s… new.
Gon lets out a sigh.
In the empty night quiet, Killua hears the faintest sound of slicked movements.
He’s doing it again.
Killua shuts his eyes and tries to ignore it. Gon deserves privacy—it’s not his fault Killua is stuck down here. A bed is where such things as this belong.
Gon moans.
He moans loud and sharp, followed by sharp tugs that ripple through the mattress above Killua’s head.
Every night before, Gon’s made noises. But none such as this. None that sounded so breathless, so desperate and lustful, thick with desire.
“Oh fuck,” Gon chokes out. “ Fuck.”
God, that sound goes straight to Killua’s dick.
His cock hardens all at once, pressing between his belly and the cool floor beneath.
Gon continues his little escapade, louder than ever before. Every second is filled with some sort of gasp and the sound of slicked skin as Gon pulls himself closer to climax. It’s agonizing—a secret symphony Killua has no right to hear, but can’t help listening to, can’t help thinking about how gorgeous he would sound if Killua were there to aid him.
He wishes he could see him right now.
He thinks about what Gon looks like; how tightly his hands are wrapped around his dick, pulling against the sensitive head, the wetness glistening on his palm. The face he’s making—how tightly his eyes must be shut as he brings himself closer to the edge.
Killua’s seen Gon in the moonlight before. But to think of his sun kissed skin glowing beneath the white light, covered in a thin sheen of sweat—
—Killua imagines himself licking a line up his thigh, settling his mouth over Gon’s crotch, breathing in his scent up close. Gon’s skin would taste like heaven, musky and salty and something entirely unique. Something that only belonged to Gon.
It sends him reeling. It makes his mouth water .
But even still, Killua doesn't look. He can’t bring himself to peek up over the edge of the bed and drink in such a delicious sight. It’d be an incredible invasion of privacy; and even though his mind is hazy with lust, he knows his limits. Still… it’s maddening to know Gon’s above him pleasing himself and he can't watch.
He wants to watch; wants to touch, to squeeze and feel and listen to Gon’s noises echo in his ear.
Killua’s nails claw into the floorboards. The wood curls beneath his nails, leaving marks in their wake.
Gon whines louder.
Killua rustles against the floor, pressing harder against it. Carefully, he moves his hips. He’s not brave enough to touch himself, not directly, anyway—that would make this all far too real for comfort. Listening without Gon’s knowledge is one thing, but getting off to it is entirely different. That’s what he tells himself, anyway: the promise he makes to himself through the want that clouds his thinking.
He’s deluded enough to ignore this is nearly crossing the line.
Killua slowly ruts against the floor, choking back a moan.
The pressure does wonders. He feels the growing ache in his gut, a rubber band stretching far too thin. Gon’s sounds are more than enough to bring him this far. He’s never been so needy his entire life. He needs to hear Gon finish, needs to hear that climaxed groan so he can go back to being fucking normal.
Gon’s tugs pick up speed. His breath is hitching now; impossibly high pitched, strung out to all hell.
Killua fucks against himself faster, matching the pace.
He needs to—he’s getting close—
“Killua.”
All at once, he comes.
Killua’s vision blacks out with stars as he juts to the finish line, body wracked with pleasure as Gon cries out above him.
There's a few moments of shared labored breathing.
Gon whimpers one final time before his breath evens out. Within seconds, the room is filled with soft snores, leaving Killua alone with his thoughts.
—
“Good morning!”
Killua’s pulled from space, blinking himself back to reality.
“G’morning,” he mumbles.
Lazily, his head rolls over to the side. His eyes are met with a small heap of fabric.
Gon’s underwear is still there. It’s completely untouched.
It all floods back to him at once.
Gon’s heavy groans.
Killua’s embarrassingly fast climax as he listened to him finish.
“Did you sleep well?”
Killua brings his hands to his face, holding his breath for just a moment.
He lets out a heavy sigh.
“You know I’m nocturnal, idiot. Of course I didn’t sleep.”
Gon hums.
“That’s right, sorry. So you were up all night? Like usual?”
Killua knows that tone of voice. It's the one Gon has when there's a mischievous smile on his lips.
He knows.
Gon knows.
Some part of Killua hoped Gon had been forgetful. He’d wanted to think Gon was unaware of what he was doing; that he’d just been making mistakes in the midst of youthful arousal. But now he knows better.
Gon’s been playing him for a fool all this time.
He wants Killua to hear him moan his name like that, the sound of it filled with want. He wants him to listen . Gon’s been purposefully getting off in Killua’s presence, dangling himself like a piece of meat in front of a starved wild animal.
This revelation leaves his mouth dry.
Gon still hasn’t come down to greet him face to face this morning. He’s staying up top, out of Killua’s reach.
“Y’know, if you ever wanted to, we could share my bed. I bet it gets uncomfortable staying down there. It’ll be tight, but we can squeeze,” Gon offers.
Killua can’t breathe.
“Oh.”
Even though Gon can’t see it, Killua ducks his head, determined to hide his embarrassment.
“That’s… uh… that’s okay, don’t worry about me,” he rambles. “I’m the monster under your bed for a reason. How else am I gonna grab you over the edge of the bed? That’s my special move. Can’t really do that if we’re next to each other.”
Killua will give any excuse. The idea of pressing up against Gon, feeling his ass against his crotch, the warmth of his body. It's too much.
His dick kicks.
Don’t you fucking dare, he begs. Don’t you fucking dare or I swear I’ll shut you in a dresser drawer or some shit. Keep it together.
“I dunno,” Gon says. “I bet you’d have a real shot at spooking me for once. You could growl in my ear or something. I bet I’d get scared. Scared enough to scream.”
Gon screaming; screaming into the fluffy pillows adorning his bed, screaming Killua’s name.
Killua wants that.
There’s a moment of silence. Killua’s teetering on the edge of a cliff, torn between scrambling backwards or taking the plunge.
Hesitantly, he takes the leap.
“Promise?”
“Promise.”
Gon’s hand reaches down the side of the bed, offering a pinky. They’ve made promises hundreds of times, but nothing like this. All those promises before had been for simple, mundane things; promises to see each other tomorrow, promises for Killua to stay, even though Gon’s far too old to have a monster under the bed. Children grow up. But Gon wanted him to stay.
Now Gon’s promising to return home and let them press against each other, promising to let Killua touch him, to growl in his ear for crying out loud.
“Sealed with… a kiss!” Gon giggles, pressing their thumbs together, blowing kissing into the open air.
Killua’s face burns hot.
After a moment, Gon lets go. His tanned legs swing over the edge, feet planting on the floor. Without saying a word, he picks up the underwear and throws it into his hamper across the room.
“I’ll make sure to leave you some chocolate for when you wake up, okay? I gotta get ready. I bet you’re tired, try to get some sleep.”
Killua hums, rolling over to face the wall. “Yeah. You’re right. I’ll see you later.”