Confessions: The Secrets of Machiko (2010) [re Up]

The Matsuoka sisters share a secret that nobody else shall ever know. Machiko Matsuoka is a high school music teacher. She live alone with her elder sister Keiko, whose legs are crippled. The two once had a good relationship until one incident in the past crippled Keiko's legs. Keiko, blaming her younger sister for the incident, began treating Machiko like a slave since then. Although Machiko blindly does whatever her sister asks of her, she cannot stop gloomy thoughts from accumulating in her heart. And Machiko comes to have a secret relationship with her student….