Geiz, a wanderer plagued by amnesia, arrives in the small nation of Orthozes with no recollection of his past beyond his name. To counter his unreliable memory, he meticulously documents experiences in a journal. He enlists in Orthozes' mercenary forces to defend against invasion by the expansionist Bjor, commanded by its ruthless leader Fract.

Despite being unable to remember his training, Geiz exhibits extraordinary combat prowess. He forges pivotal bonds with fellow mercenaries: Mara, a Crimson Knight of Orthozes who witnessed Bjor slaughter her parents in childhood, and Dino, a demonic warrior fighting to support his daughter Pururu after Bjor soldiers murdered his wife. Together, they repel Bjor's assaults.

Geiz's physical resemblance to Fract sparks confusion and conflict. Early in the war, Bjor soldiers mistake a child for Geiz due to this likeness, killing the child—an act highlighting Fract's brutality. This similarity later unveils Geiz's origins: he is a clone or artificial construct of Fract, created by the godlike Mugen. Their intrinsic connection drives the narrative toward a climactic confrontation, where Geiz and Fract grapple with shared roots but opposing destinies.

In their final battle, Geiz asserts his individuality against Fract, redefining both characters and prompting Fract's partial redemption. A post-credits scene casts ambiguity on Geiz's true nature and role in the conflict, hinting at unresolved questions about his identity and the war's consequences.