This manga adapts Toshihiko Tsukiji's light novel about Natsuru Senou, an ordinary second-year high schooler chosen without warning to become a Kämpfer, a fighter who transforms into a girl the moment a colored Bracelet of Oath activates. Blue Kämpfer Akane Mishima and Red Kämpfer Shizuku Sangou draw Natsuru into their truce and their fights against rival factions, all while he tries to keep the transformations secret from everyone else at school.