In order to save her brother who attends an all-boys school from being bullied, Mahiro, the older sister, disguises herself as a boy and sneaks into the school, where she is able to get a hold of the bullies' weaknesses and stop the bullying. However, when the bullies find out that Mahiro is a girl, they retaliate by raping her. At first, Mahiro is strong-willed, but gradually she falls into the pleasure of being abused, and becomes addicted to lust and goes wild...