So GOOD

lmao I hope he rots in hell. He was an abusive fuck who left Yuki to die alone in the snow and only cares/wants Yuki now that he's lonely. He's a total loser and a bastard. He abused Yuki and hurt him so much.

I don't think it was implied he was raped by that man, it was seeming to imply he's a man now because he could pursue his goals even if they meant having to do something like killing a man who raised/was like a mentor or father to you. Basically, that whole story is to show how selfish he is as a character and his disregard for other's lives and emotions in the wake of his own and in his ambitions and desires. He's a selfish person. Thats the moral of his story.

I wholeheartedly disagree and think you're being really biased here, he "left him in the snow" to get him out of the life, they talk about how the cut wasn't fatal. Their relationship didn't seem bad either, they seemed pretty close, not sure what you mean by he "abused him". We'll just agree to disagree here, you're ignoring 3/4 of the context of their relationship and only focusing on the neck wound. Even there you're ignoring the reveal that the cut purposely wasn't fatal. Also, it definitely implied the guy used to rape him... read through there again...

He comments on how he's a man now after going into a creepy monologue to Tatsuo about how he likes to fuck boys because they're not quite men yet, but not women either. He likes entering them and "touching the man inside". He likes to imagine he's tainting their manhood. Then, after the monologue and after he comments on him being a man now, the boss says "you were a favorite of his when you were a child". You think he was the only boy that rapist didn't rape? He seems to be considered attractive too.