Yuwa, the strong-willed and somewhat selfish older sister, and Chiharu, the quiet and weak-willed younger sister. The two were having tea in the living room and complaining about each other's boyfriends. When Yuwa heard from Chiharu that her boyfriend's sex was too rough and she was having trouble with it, she felt a little jealous and became interested in the boyfriend. So Yuwa asked Chiharu, "Shall we swap boyfriends?"...