The Usagi brothers lost their parents when they were young. Her older sister Aika continued her efforts and graduated from a junior college and became an office lady. On the other hand, her younger brother Masakazu was playful and didn't study well, but Aika was very fond of Masakazu, her only family. One day, Aika receives a phone call from a man named Kudo. "Your younger brother made a mistake on our group's sister." In order to make a mistake for her, Aika is kidnapped by Kudo and others, and she is subjected to humiliation.
