Ayumu　is a shy and innocent boy. Touka was in the past his teacher, but nowadays is his stepmother, Ayumu always loved Touka and he is happy in to have her like a mother. Someday happened a sex education class in his school, but he do not understand nothing. In home Ayumu asked to Touka about sex, concerned about the fact that is looks painful, since he once see Touka making sex with his father and she looks n pain. Touka say that sex is not painful and asked to masturbate Ayumu to proof that this is not painful. After ejaculate, Ayumu enter in panic because of fist time see semen, and he thinks that he is sick. To proof to Ayumu that he is health and no sick, she offer to make anal sex with him. He accept and the secret anal sex relationship between the two start.