The plot revolves around Natsuru Senō, 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 "Kämpfer", a female fighter. The Kämpfer are destined to fight with other Kämpfer. The story starts when he is attacked by an unknown girl who happens to also be a Kämpfer.