Mami, an older sister who is inexperienced and lacks knowledge about sex, was troubled because her boyfriend didn't seem to be enjoying himself. Her younger brother, intending to comfort her, got involved in her consultation. For his sister, who had never closely observed a penis, he decided to let her observe one. However, both of them became excited and ended up with handjobs, blowjobs, and ejaculation. From that day on, the younger brother became her practice dummy. Although they both thought it was wrong, Mami complied for the sake of her boyfriend. On the other hand, the younger brother, wanting to have sex with his sister, used every trick in the book to please her, ultimately crossing the line...
