By now, it is instinct.
He can deny it, refuse its existence and throw it away, but it will always return to him. Trust him, he's tried to get rid of it, pass it on, break it – but it never leaves. It simply finds a way to return to him, despite the circumstances. He's screamed because of it; he'd never asked for this burden to bear! He didn't want to be the 'key,' or whatever he's supposed to be. He never wanted to save the world, team up with two talking animals, out of all things, and lose his two best friends in the process and therefore have to find them once again.
Sora grips the handle of the Keyblade, the flesh covering his knuckles whitening. Sometimes, he craves blood and destruction and chaos. That isn't him, it isn't him, he doesn't want that! But he does, and oh, he does, and the craving is so hard to resist. It nearly kills him each time, to smile at that goddamn duck and act clueless. To protect. To serve. It kills him, and he wants out, but he can never get out.
The one possessing the Keyblade should not have these thoughts, these dark, horrible thoughts that imagine a human body mangled by their own hands. They should be light, represent light, practically be an angel fallen from heaven and pretty near being perfect. They should value friendship most, and their safety, instead of being entirely selfish and nothing more.
He is slowly losing himself to this new world he's found himself wrapped up in, and Sora cannot find his own way out. The Keyblade is warping him, destroying him from the inside out, and there is no saving him. There is no antidote, no magic words, no battle strategies that can stop this almost-disease from spreading.
By now, it is instinct for him to attack, and it is instinct for him to hate.
He wonders how much of him is left.