Houkago no Hoken'i ~Ane Juujoku~

Mai is a sick-room teacher. She enjoys her life at school, but there is one thing she concerns. It's her younger brother, Tomohiro, a student at the same school. He is so wimpy, and comes to the sick-room quite often. One day, a student comes into the sick-room. That is Takuya, Tomohiro's classmate. He suddenly tries to rape her. She resists it at first, but he says, "Let me shag with you, and I'll stop teasing Tomohiro." She finally sleeps with him, but this is just the beginning....

[From ErogeShop]