This role-play is performed by adults. Ayumu, who enrolled in a preparatory school in Tokyo, is not good at living together in the school dormitory, so she is allowed to live with her sister, a gal who lives in Tokyo, but her older sister, who is a gal and a slut, is constantly bringing various men into her room and having sex with her, so Ayumu, an adolescent who is curious about naughty things, is so worried that she can't study.