12 Volumes (Complete); 15 Volumes if you include the half volumes 8½, 9½, and 10½.
The plot revolves around Natsuru Senou, a normal high school boy with blue hair. One day he wakes up to find himself turned into a girl. A stuffed tiger “Harakiri Tora” comes to life and tells him to fight as a female fighter “Kämpfer”. Having no idea about what’s going on, Natsuru is involved in many battles against other female Kämpfer.