"I" was visiting my girlfriend's house today. In the middle of the day, I started drinking with my girlfriend (a university student) and her sister (an office lady) in the living room. After a while, she got drunk and fell asleep on the sofa. I had no choice but to relax next to her, when suddenly, in the dining room opposite, her sister started taking off her clothes. Despite my surprised eyes, she tied herself up with hemp rope and showed me how she masochistically masturbated, and even begged me to train her...