Sadistic Yoga(2007)

The female instructor Mariko gives yoga classes at a high-class club in Tokyo. She has a crush on Rika whom she gives private lessons to. When she notices bruises on Rika's body, Mariko learns that the young woman is involved in a highly abusive S&M relationship. On order to gain the affections of her student, Mariko decides to take revenge against the men in Rika's life.