"Kämpfer" is a manga series written and illustrated by Toshihiko Tsukiji, with character designs by Senmu. The story centers around Natsuru Senō, an ordinary high school student whose life takes a dramatic turn when he is suddenly transformed into a female warrior known as a Kämpfer. This transformation occurs after he is chosen by a mysterious entity to participate in a secret battle among Kämpfers, who are individuals granted special powers to fight one another. The Kämpfers are divided into two factions: the Blue Kämpfers and the Red Kämpfers, with Natsuru being assigned to the Blue faction.

Natsuru's transformation into a female Kämpfer is involuntary and occurs whenever he is drawn into combat. This duality creates significant challenges for him, as he must navigate his daily life while concealing his Kämpfer identity. The series explores themes of identity, gender, and the complexities of relationships, as Natsuru struggles to reconcile his male self with his female Kämpfer persona. His best friend, Sakura Kaede, becomes a central figure in his life, as she is also a Kämpfer, though she remains unaware of Natsuru's dual identity for much of the story.

The narrative introduces a variety of characters who play pivotal roles in Natsuru's journey. Shizuku Sangō, a stoic and skilled Kämpfer, becomes both an ally and a rival, while Akane Mishima, Natsuru's childhood friend, develops romantic feelings for him, further complicating his situation. The series also features Mikoto Kondō, a classmate who harbors a secret crush on Natsuru, and a mysterious white stuffed animal named Moderator, who serves as the overseer of the Kämpfer battles.

As the story progresses, Natsuru becomes entangled in a series of battles against Red Kämpfers, each encounter revealing more about the nature of the Kämpfer system and its enigmatic rules. The series balances action with comedic and dramatic elements, often highlighting the absurdity of Natsuru's predicament. The battles themselves are intense and strategic, with each Kämpfer wielding unique abilities tied to their personalities and backgrounds.

The manga delves into the psychological and emotional toll of Natsuru's dual existence, as he grapples with questions of self-identity and the morality of the Kämpfer battles. The relationships between the characters evolve over time, with alliances shifting and secrets being uncovered. The series also explores the motivations behind the Kämpfer system, hinting at a larger, more sinister purpose behind the seemingly arbitrary battles.

"Kämpfer" combines elements of action, comedy, and romance, creating a narrative that is both entertaining and thought-provoking. The manga's exploration of gender identity and the fluidity of self-expression adds depth to its otherwise lighthearted tone, making it a unique entry in the genre. The story concludes with a resolution to the Kämpfer battles, though it leaves room for interpretation regarding the characters' futures and the true nature of the system that governed their lives.