Sukebe kyôshi: Hikinuku kaikan!.

Miyoko is temporarily assigned to a certain high school in place of a teacher who is absent due to childbirth. On her first day of school, she finds her student Mitsuru smoking a cigarette behind the school building. However, Miyoko doesn't blame her, she just says that she was similar to her high school days, and she leaves. One day, Mitsuru sees her homeroom teacher, Tsurumi, and her student, Natsumi, hugging each other in the gymnasium. Mitsuru was shocked and was smoking a cigarette on the rooftop. Miyoko then went to the nurse's office...