[Rocomani (Manatsu)] Darashinai Imouto ni Kareshi ga Dekitara [Digital]

If you want the full explanation. Little twin sister is gaming while spending time with her boyfriend. It's mentioned that she has an older twin brother to establish him to the reader but that they're pretty different. She gets horny and starts masturbating then sees someone come in her room, realizing it's her boyfriend and that she's embarrassed she covers her face with her blanket. Her boyfriend than starts fucking her raw. Finally after a few minutes she flips over to find out, SURPRISE, it wasn't her boyfriend but her older twin brother. She begs and begs him to stop but it feels so good she's barely coherent. Finally he cums in her and she orgasms pretty hard. He calls her a pervert who gets off to being raped by her brother and leaves. She cries a bit but in the end she can't stop masturbating hoping her brother rapes her again and apologizing to herself that her boyfriend will never be good enough

@wespar , tq for explanation :'3

Raping your twin sister to steal her away from her new boyfriend is fairly peak entertainment.