"I" came to her house today. In the daytime, the three of us, me, my girlfriend (a college student), and her sister (office lady), start drinking at home in the living room. After a while, she fell asleep on the sofa because she was drunk. I had no choice but to relax next to her sleeping girlfriend when her sister suddenly took off her clothes in the dining room opposite. - Despite my surprise, my sister showed off masochism while tying herself with hemp rope and begged me to train her.