Yuu, a strong and a little selfish sister, and Chiharu, a younger sister who is quiet and weak to push. The two were complaining about each other's boyfriend while having tea in the living room. Yuu was a little jealous when she heard that her boyfriend's sex was too intense and she was in trouble because of Chiharu, and she became interested in her boyfriend. So Yuu asked Chiharu, "Would you like to exchange your boyfriend?"