A/N: Ahhh I'm sorry. I saw a few people talking about this idea on my blog and I just couldn't resist! So here, have some terrible no-happy-ending angst and try not to hate me when you finish reading it.
Gon can't believe it. He can't and he won't and he refuses to because it's absolutely not true, not true at all, and he can't think and he can't feel he only knows that it's a lie, a lie.
Killua can't be dead.
It's not possible.
He can't be.
"Liar." The word rips itself from Gon's throat, low and guttural, and suddenly he can feel the cold stone under his knees, the wind whipping itself against his back, the tears still slipping down his cheeks. And the pain. Oh god, he hurts so much, like somebody is squeezing every last drop of life from his body and he wants to cry and scream, to pull his heart form his chest because maybe then it will all stop and he won't feel like his blood is poison, eating away at him from the inside out.
The wind picks up and Killua's body slumps, pale skin mutilated, eyes dim. Lifeless.
Pitou says his name, turns and offers him a hand but then curls their fingers. "I have to kill you," the say and Gon snaps.
His best friend is dead. The boy with a dark past and a bright smile, loyal and faithful to the very end and it's Gon's fault but it's also Pitou's. Killua who would have followed him to the edge of the world and back, Killua who was always there for him, Killua who was uncomfortable with kind, soft words but who deserved them more than anyone else on the planet. And he was dead.
Dead. Dead. Dead. Dead Dead Dead Dead dead dead dead dead deaddeaddeaddeaddeaddeaddeaddeaddead….
Gon stands. The candles on the mantle flicker and he can feel something terrible, something big, building deep in his gut. It's all consuming and it's dangerous but he doesn't care. Doesn't care because he needs Killua and Killua's gone and both he and Pitou are to blame and he has to do something about it, can't just leave things as they are.
The thing grows and it burns and rips Gon apart and builds him anew and he knows there's going to be a heavy price to pay but he just doesn't care.
He's got enough sense that he knows he doesn't want to fight here, not in front of Killua, not in these cold, stone halls or the wide, dark rooms. So he leads Pitou outside and it's odd, it's different, the shift of his muscles and the weight of his body. It doesn't matter.
The night air is warm and thick, a balm against Gon's burning skin but it doesn't take long for Pitou to try an attack from behind. Gon simply sidesteps and then drives his foot up into their stomach. It's a powerful blow and if he wasn't so lost he might have marveled at it, at his abilities in this state, but he is and so he doesn't.
When Pitou careens back towards the Earth, spinning head over tail, Gon is ready with janken. He doesn't blink when he feels the power burble under his skin as his fist meets flesh, a rushing brook that's going to overflows its banks any minute. He follows Pitou farther into the dense trees.
The fight, if you can even call it that, is over quickly. Pitou's body breaks and crumples under his blows, weak as wet paper where before there was only hardened strength.
He stops but only because the scent of the ant's blood, blue and thick, is nauseating. It's slick against his skin, uncomfortably hot. He's not expecting Pitou's body to move again, for those sharp claws to come whistling through the air, the thing headless but still covered in nen.
The claws sink through his chest, the fingers they're connected to grasping, pushing, trying to pierce into and through him. He grabs the body with one hand, pulls its bloodied appendages out of his skin, and delivers another series of janken with all the strength of his newfound body, the river within him overflowing its boundaries in one roaring wave.
It stumbles back (because it's no longer Pitou, merely a puppet) and then drops to its knees. Gon gives it one last blow, a spinning kick with all of his nen focused into the point of contact and he knows it's over. For both of them.
The body shudders and falls, sickly pink nen dissipating into the air.
Gon's knees hit the dirt. He sways and feels all his seams burst simultaneously, the power he'd forced inwards in order to mature himself gushing out in unsteady heaves. It rips apart the very body it had made and Gon knows he can survive this, can survive the backlash of his own stubbornness and heartache. But he doesn't want to, because Killua is gone and maybe he never found his father and maybe Aunt Mito will miss him but. Killua. Is. Gone. And no matter what he does now, no matter where he goes, that ghost will forever haunt him.
With the last of his strength Gon tips his head back, spreads his palms and lets his own power devour him.