In order to save her younger brother, who attends an all-boys school, from being bullied, her older sister, Mahiro, disguises herself as a man and sneaks into the school, grasping the bullies' weaknesses and being able to stop the bullies. However, Mahiro is counterattacked by the bullies who discover that Mahiro is a woman. At first, Mahiro is optimistic, but gradually falls into masochistic pleasure, drowning in lust and being disturbed.