Natsuru is selected to be a Kampfer. The catch: all Kampfers are female, and Natsuru is male - at least he was!.

The plot revolves around Natsuru, a normal high school boy with blue hair. One day he wakes up and found himself turned into a girl. A stuffed tiger "Harakiri Tora" comes to life and tells him that he has been chosen as one of the "Kampfer", a female fighter. The Kampfer are destined to fight with other Kampfer. The story starts when he is attacked by an unknown girl who happens to also be a Kampfer.