Mako, a daughter whose mother was hospitalized due to illness and came to her parents' house to help with housework. When I was chatting with my father, my younger brother came back there, but his attitude was awkward. When Mako, who was interested, looked into the room, she found out that her younger brother had purchased Onahoru. Mako realizes that he is a virgin because he doesn't know how to use it, but he makes fun of him, but he is overwhelmed by the power of adolescents. From that day on, I was struck by my younger brother's sexual desire.