Ayumu is a shy and innocent boy. He always loved his teacher Touka and he is happy to have her as his "stepmother".

His class held a Sex Education class one day but he understood nothing, so he decided to ask Touka about sex, concerned about the fact that he once saw her having sex with his father in pain. Touka said that sex is not painful and asked Ayumu to masturbate to prove that it is not painful. After ejaculating, Ayumu had a panic over seeing his semen for the first time, and he thinks that he is sick. To prove Ayumu that he is healthy and not sick, she offered to have anal sex with him. He accepted and they started a secret anal sex life.