Why was the family erased?

When the suspect of an arson case refuses to cooperate with the investigation, the detectives search his house and find a locked-up little girl. She doesn't talk and there are no clues to her identity, so assistant psychology professor Narumi Saku is asked to counsel her.

High school girl Madoka may look pretty and cute, but there is another side to her. She can exact revenge, land a good punch or a kick and not care about limits. She opts to inflict pain, coerce and blackmail a virgin when she is sensually touched on the train. She begins making his life hell.