SM kyôshi: Oshiego ni shibarete(1996)

Overview:

Miho, a female teacher, feels bored in her relationship with an ordinary office worker and complains to Ezaki. This leads to Ezaki forcing her into a physical relationship, and from then on he starts forcing her into sadistic sex, but she finds herself getting very excited by it...She continues to indulge in her carnal desires every day, but one day she is finally seen by a student. At first he is shaken by the act of his admired teacher, but Ezaki encourages him...