For some guys, the idea of waking up as a beautiful girl would be a dream come true. But for Natsuru, who suddenly finds himself transformed into a girl and informed by a stuffed tiger that he is now a Kampfer - a mystical fighter who must engage in battle with other Kampfers, also in female form - life becomes a nightmare. In addition to the obvious physical changes, Natsuru's childhood best friend reveals that she has feelings for his new female body, complicating things further. As if that weren't enough, Natsuru's school is separated into boys and girls sections, leaving him with dual enrollment and rumors flying that he is dating himself. To make matters even more perilous, there are other Kampfers attending the school who want to take Natsuru out - some in a romantic sense, and others with the intention of permanently ending his life. Oh, and some Kampfers have weapons like swords and guns. As Natsuru navigates this new world, he must fight not only with his fists, but with his hormones and other body parts as he becomes a gender-bender defender, fighting for his life as a contender in the Kampfer battles.