Zange -Matsuoka Machiko no Himitsu-

Machiko Matsuoka is a high school music teacher who lives with Keiko, her older sister with a bad leg. They were close once, but Keiko became disabled in an incident. Believing that Machiko was the cause, Keiko has treated her like a slave ever since. Machiko has done everything she says, but her frustration has accumulated. One day, Machiko begins a secret relationship with her student.