Momiji (Hoshimi Rika) is an ordinary student attending a cram school. She has a boyfriend who is also a fellow student, but she is still a virgin. The man she is in love with is her unrelated older brother, Akihiko, who is not related to her by blood, but who has remarried after being taken into custody... Since their parents died in an accident, Akihiko has been working hard to get his younger sister, Momiji, into college, and lives with his wife, Kanae (Kuroki Ayumi). Akihiko's wife, Kanae, is jealous of the delicate relationship between the siblings, and moans every night about their intense sex life so that Momiji can hear. Momiji's feelings for her brother grow stronger each day, and she takes a certain sexual action...