Shin Kyouhaku 2 The Animation: Kizu ni Saku Hana Senketsu no Kurenai(2006)

Akehime Saki is a beautiful girl with an English mother. She has a secret: she is going out with her teacher, Tsuge Akito, and the immorality of their secret excites her. However, there is a person prying into their affair. One day, Saki receives a phone call: "do not meet the man again, or else..." Although the phone call raises suspicion in her, she goes out with Akito once more, not knowing there is a shameful trap waiting for her...