(A/N: This is an odd little piece that's been stuck in my head for awhile. I'm not even sure why I wrote it, except that I love the relationship between Gon and Killua and I think it kind of blurs the lines of definition between siblings, friendship, and romance. I tried to capture all of that in here. This is based off the gag in the Hunter Exam arc where Gon worries that Killua will not want to room with him because he's such a restless sleeper)
After the first few nights they spend in the same room, it becomes a big joke between them, how they thrash around in their sleep. At that age, with that new a friendship, anything can be funny. It's less funny the first few times Killua wakes up with teeth marks on him. Gon swears to know nothing about them.
When the Exam ends and Killua is abruptly gone, Gon discovers he misses having his head kicked in the middle of the night.
Sometimes, instead of sleeping, they stay up talking. It's only when Gon is tired that he admits to any uncertainty that he will ever find his father, or be welcomed when he does. Sometimes it's just light chatter, though, about video games and people they both know or something weird they saw that day.
Sometimes, Killua wakes up disoriented, and before he can remember where he is or who he's with he's ready to strike. It never wakes Gon up. Killua makes himself feel better by pouncing Gon instead of hurting him, and then Gon does wake up and complains and pushes Killua, and they wrestle each other before going back to sleep.
Eventually Killua stops feeling disoriented when he wakes up, but the pouncing habit remains. He swears he's doing it to help Gon train.
Even ordinary boys can break the bedsprings by jumping on the bed; adolescent boys armed with Nen can break the ceiling, too. They are not welcome back at that hotel.
At some point, Killua stops pouncing so much. Instead, he starts glomping onto Gon in the middle of the night, without (he swears) ever waking up. Gon thinks it's funny. He'll just be lying there and suddenly, a tangle of limbs will be caging him and Killua will be breathing into his ear. Sometimes it's fine, but sometimes he thinks Killua has more than his fair share of elbows.
The really odd thing about it is, it doesn't wake Gon up anymore. If he's still drifting in and out of sleep he notices, but if he's already asleep he won't know he's been glomped until he wakes up in Killua's possession the next morning.
At first when they break something at a hotel, Gon and Killua stand side by side with their most earnest expressions in place as they try to convince the staff of the truth: that it had been a wrestling match-the G rated kind, Gon would hasten to add-and nothing inappropriate for two boys as young as they were, that had broken the bed.
After the first few times, though, Gon finds himself alone in his attempts to make the truth be heard, while Killua grins and winks at the staff and generally makes things worse.
Even after Biscuit teaches them to wake at even the slightest change in their surroundings, Killua can still glomp Gon without him waking up, or pounce him and be on the other side of the room before Gon knows what's happened. It isn't fair, and it's even more unfair that Killua won't tell Gon how he does it. Trying to stay up and catch him at it just makes Gon tired. He sometimes wishes his best friend didn't have quite the taste for mischief that he does.
At home, Mito always sets up a cot for Killua next to Gon's childhood bed, and Gon always makes sure to step on Killua when he gets up to go to the bathroom, and sometimes gets tripped in return. One year they've both grown and neither bed fits them anymore, so they pile blankets on the floor. Killua has almost always glomped Gon by morning. He swears he's always asleep when he does it and it's never intentional.
One time, they are separated. It is not a good separation; it has a great deal to do with Killua's family and what they will and won't permit, and what he does and doesn't believe about himself.
On their first night back together, Killua goes to his own bed and doesn't say much, answering Gon's questions in monosyllables and pulling the pillow over his head. Eventually Gon stops trying to make conversation, and Killua falls asleep. When he wakes in the middle of the night Gon is more or less on top of him, pinning him to the bed with his heavier weight, and so deeply asleep he's drooling-thankfully onto the pillow, not Killua. Killua tries to squirm out from under him, but Gon is stubborn even asleep, and pushing or yelling his name doesn't do any good. Killua finally has to administer a small shock with Nen before Gon wakes up and lets him get up to use the bathroom. When he comes back to bed, Gon wraps himself around him and says in a slurred voice, "Don't go anywhere, okay?" before losing consciousness again.
"Not like I could," Killua mutters, and resigns himself to the concept that Gon will be sleeping on top of him until he is confident that Killua will not leave again.
They stop asking for a room with two beds, because between Killua's unconscious glomping and Gon's very conscious anchoring of Killua, they always wind up in the same bed by morning anyway. People assume they're dating. Gon and Killua correct them sometimes, but sometimes let it go. They thrash around less than they did when they were younger; they figure they're growing out of it. Accidental injuries still occur, but they're less frequent.
Sometimes Gon talks in his sleep and tells Killua not to leave him. Sometimes he talks in his sleep and tells Killua to slay the marauding pirates with ketchup, or stop stealing his chocolate soup. Killua thinks he preferred the thrashing.