"Orga Mania" is a manga series that blends elements of science fiction, action, and psychological drama. The narrative centers on a dystopian future where humanity is on the brink of extinction due to the emergence of monstrous creatures known as "Organs." These beings are the result of a failed scientific experiment aimed at enhancing human evolution, leading to grotesque mutations that now threaten the survival of the human race. The story unfolds in a world where society has collapsed, and remnants of humanity struggle to survive in fortified cities while battling the Organs that roam the wastelands.

The protagonist, Kaito, is a young man who becomes entangled in the conflict when his sister is kidnapped by a powerful Organ. Determined to rescue her, Kaito joins a specialized military unit known as the Organ Hunters, a group of genetically enhanced soldiers tasked with eliminating the Organs. As Kaito undergoes experimental procedures to gain superhuman abilities, he discovers that the line between human and Organ is far more blurred than he initially believed. His journey is marked by internal conflict as he grapples with his own humanity and the moral implications of the experiments that created the Organs.

Key characters include Dr. Akira, a brilliant but morally ambiguous scientist who played a pivotal role in the creation of the Organs. Her motivations remain shrouded in mystery, and her actions often blur the line between ally and antagonist. Another significant figure is Rina, a fellow Organ Hunter with a tragic past, whose relationship with Kaito evolves from rivalry to mutual respect as they face increasingly dangerous threats together. The series also introduces a variety of Organs, each with unique abilities and tragic backstories, adding depth to the conflict and challenging the characters' perceptions of right and wrong.

The plot is driven by a series of escalating battles between the Organ Hunters and the Organs, interspersed with moments of introspection and ethical dilemmas. As Kaito delves deeper into the origins of the Organs, he uncovers a conspiracy that implicates the highest levels of the surviving human government. The narrative explores themes of identity, the consequences of unchecked scientific ambition, and the struggle for survival in a world where humanity's greatest enemy may be itself. The story builds toward a climactic confrontation that forces Kaito to confront the true nature of the Organs and his own role in the ongoing conflict.