Natsuru Senou, an ordinary high school student, finds his life drastically altered when he wakes up one day transformed into a female version of himself. This sudden change is accompanied by the appearance of a mysterious bracelet and a talking stuffed animal named Mishiro, who informs him that he has been chosen as a Kampfer—a warrior tasked with fighting in a secret battle between other Kampfers. These warriors are divided into two factions: the Blue Kampfers and the Red Kampfers, who are locked in an ongoing conflict. Natsuru learns that his transformation into a female is a necessary condition for combat, as Kampfers can only fight in their female forms.

As Natsuru struggles to adapt to his new reality, he discovers that his classmate, Shizuku Sangou, is also a Kampfer, though she belongs to the opposing Red faction. Despite their initial rivalry, Shizuku becomes a key figure in Natsuru’s journey, offering guidance and occasionally assistance in battles. Another classmate, Akane Mishima, harbors romantic feelings for Natsuru but is unaware of his Kampfer identity, adding a layer of complexity to their interactions. Meanwhile, Kaede Sakura, a close friend, becomes suspicious of Natsuru’s frequent disappearances and erratic behavior, further complicating his efforts to maintain secrecy.

The series explores Natsuru’s dual life as he balances his ordinary high school existence with his responsibilities as a Kampfer. Battles between the factions are intense and often involve the use of specialized weapons and abilities unique to each Kampfer. The narrative delves into themes of identity, as Natsuru grapples with the implications of his transformation and the expectations placed upon him as a warrior. The relationships between the characters evolve as alliances shift and secrets are revealed, creating a dynamic interplay of trust and conflict.

Throughout the series, the origins and purpose of the Kampfers remain shrouded in mystery, with hints of a larger organization orchestrating the battles. Natsuru’s journey is marked by a series of confrontations with powerful opponents, personal revelations, and the gradual uncovering of the truth behind the Kampfer system. The story combines elements of action, comedy, and romance, with a focus on the challenges Natsuru faces in navigating his dual identity and the impact it has on his relationships and sense of self.