Waking up transformed into a beautiful girl might be the stuff of some guys’ fantasies, but when the suddenly effeminatized Natsuru is informed by a stuffed tiger that he’s now a Kämpfer, a mystical fighter who has to fight other Kämpfers in female form, his life becomes a living nightmare! Putting aside the obvious “plumbing” issues, Natusru’s best childhood friend turns out to swing the other way and SHE has a crush on his new female body. Not complex enough? Natsuru’s school has separate sections for boys and girls, so he and she are now double enrolled. The rumor-mill has it that he’s dating herself. And there are other Kämpfers attending the school who want to take her out, and he’s not sure which ones mean “on a date” and which ones mean “permanently.” Oh, and did we mention that some Kämpfers use SWORDS and GUNS?! Hormones, fists and other body parts will fly as the daring, new gender-blender defender must become a contender or die!
Natsuru Sen wakes up to discover that he has turned into a woman. A plush animal tiger comes alive to tell him that he is a Kämpfer, which must do battle with other Kämpfer. Since Kämpfer can only be female, he was transformed.
Natsuru stops Akane from shooting Kaede, and the attacker escapes when the bell for class rings. Natsuru realizes that the enemy also goes to his school and becomes embroiled in the struggles between the Kampfer.
Natsuru begins his first day in the girls side of the school. He becomes very popular among the girls. Kaede confesses her love, but things go pear-shaped when rumors that his male form is dating his female form start spreading.
As the cultural festival comes up, Natsuru is shocked to find that Shizuku has entered him into the Miss Seitetsu beauty contest. Deciding to go with a karaoke act, Akane, Kaede, and Shizuku decide to enter the beauty contest too.
The cultural festival is about to begin. In the changing room, Kaede gets into an argument with Akane. Male Natsuru later meets up with Kaede, and gives her some encouragement, although she still considers him a rival.
Natsuru is surprised to find his childhood friend Mikoto has returned. When Kämpfer Natsuru heads to school, she is forced to participate in a maid café event. She is later accompanied by Shizuku, who warns her that a new Kämpfer will be coming.
Natsuru, unexpectedly accompanied by Akane and Shizuku, arrives at Kaede's house. Kaede shows everyone her collection of Entrails Animals, including a prototype. As Natsuru tries to go to sleep, he accidentally transforms into his male form.
Shizuku asks Natsuru to go out on a date. While Shizuku insists that it's a proper date, Natsuru goes along thinking it is a plan to draw out the White Kämpfer. After the aquarium and a picnic, Shizuku questions him about Kaede.
Akane is having a romantic summer date with male Natsuru at the pool. However, Mikoto, Shizuku and Kaede show up as well.
Natsuru finds himself sitting next to Kaede outside the hotel, who hypnotizes him into making Shizuku his. Natsuru, who can't remember anything after leaving the room, is confronted by Akane, Shizuku and Mikoto in their Kämpfer forms.
Shizuku invites Natsuru over to talk about Kaede, getting Kaede's Burnt Alive Lion to spill the truth about the Kämpfer system. Her friend Tamiko was killed in a Kämpfer battle, she has sworn vengeance against those responsible for Kämpfer combat.
Natsuru wakes up on Christmas Eve morning to find out that he and his messenger, Disemboweled Tiger, have swapped bodies!