Nishina

Nishina is just a normal girl that goes to school, but one day she hears her classmates talking about a student thas has sexual relations with whoever asks him to. Pulled by the curiosity she asks him to do so, and ends up loving it so much that she makes some adds for people to meet her and have sex again. It starts out as simple curiosity. She has a mediocre first experience with a classmate, her teacher awakens her to her desires, and eventually she "keeps" a rapist to satisfy her carnal desires. She is past the point of no return, and that's completely fine with her.