Younger sister Mayu and older brother Kenji attend the same school. The two of them secretly had a physical relationship. However, my younger sister is a so-called tsundere who behaves strangely around her brother on the outside. One day, Kenji heard a rumor that Mayu had a boyfriend in her class. Kenji couldn't contain his jealousy, took Mayu everywhere and had vaginal sex everywhere in school.