Responses
Hm, it was hint dropped that she was mean from the beginning in the story. Which could have in turn twisted the uke's psyche... OR maybe as the story goes on, we'll see if it was as a result of everything or he was always that way.
Tbf, I don't like either, but I do hate the sister for leading Seme on just to use him/also spite the brother.

I don't hate the sister. Fuck Felix for being a creepy, manipulative and opportunist asshole. Yeah, the sister is mean and a dick but, did she EVER tried to kill his brother or steal his persona to benefit herself? No. That's it.