Roxas could see everything. He watched what Sora did, what he saw, what he tasted, what he thought. He didn't own anything; he was merely an extra soul trapped in another's body.
He would never be whole.
So technically he wasn't there. He may have existed, if vaguely, but he was never there. He was an onlooker in Sora's life, an outsider in his body, viewing, watching, reading, seeing, smelling, tasting, thinking. All he could do was breathe and watch and sit and do nothing.
He would never completely exist. Not when he was a Nobody.
There were others like him. He could see them. Through his special eyes, he saw everyone else's Nobody, and they saw and watched and thought like him. Through different perspectives, a different mindset than his Somebody. His thoughts weren't his, his experience wasn't his, and he would never own anything that was worth value.
Roxas never liked Sora. In his own special mind he had that was disconnected from Sora's, he imagined horrible things. Drowning, water filling his mouth as he sunk to the bottom of a pond, lake, ocean. Roxas envisioned himself watching happily, smiling and humming as he thrashed and swam and sunk and died. Then he would be real. The he would be free.
He saw Sora burning. Hair disintegrating, skin melting, charring, his brain turning to mush from the heat.
He saw Sora being butchered. Strapped to the cutting board, helpless, as Roxas got out the knife and sliced away flesh, bone, marrow, more and more and more skin till they were thin strips leaking red. He'd take Sora's eyes - the eyes that copied his - and squeeze them in his hands until they were liquid. He wondered was they would look like, liquid eyes spilling through his fingers like sand.
He saw Sora falling, falling, falling off a cliff. He tripped, and Roxas would be there, watching and smiling and humming as if he won the lottery. In his imagination, he did. He'd watch Sora fall and scream and try to live as his bones crunched and split and died on impact with the ground. He'd watch his body turn to a bloody mess on the ground below.
He saw Sora being ripped apart, seeing himself crawl out of his heart and through his ribcage, listening as his bones crunched and organs squished and he'd be in so much pain that Roxas would stare at his writhing body and laugh and laugh and maybe kick at him. It was all pretty to him.
Roxas wondered if he could rip his way through Sora. That would be fun. Painful for Sora, excitement for Roxas. Roxas liked how it would have ended. The fantasies painted beautiful pictures and flashes of reds and blacks and screams and pleads. Roxas loved the fuzzy and warm feeling weaving through his veins like spider webs.