Reiko, an aunt who takes care of her relative Shinya and even helps him with his studies. Reiko teaches a wide range of subjects, including Japanese, English, mathematics, health and physical education, and art, but she especially teaches health and physical education with more enthusiasm than necessary, using her own body. In fact, Reiko herself is sexually frustrated and secretly enjoys health and physical education time with Shinya. And under the pretext of sex education, Reiko ends up having an indecent relationship with Shinya, not as an aunt but as a woman.