Aide awakens in Orthozes as an amnesiac wanderer, retaining only his name. To combat his memory loss and inability to form new recollections, he meticulously documents events in a journal. Despite his condition, he possesses extraordinary combat prowess, leading him to join a mercenary band defending Orthozes against invasion by the militaristic nation of Bjor. His companions include Mara, a disillusioned former Crimson Knight, and Dino, a demon fighting to support his daughter after his wife's death.

Aide bears an uncanny physical resemblance to Fract, Bjor's ruthless leader who seeks to conquer Orthozes and surpass his father's earlier failed attempt. This likeness becomes central to the mercenaries' strategy: infiltrate Bjor's forces and assassinate Fract. As conflict intensifies, Aide experiences fragmented memories and unexplained connections to Fract, fueling his desperate search for identity.

The climax reveals Aide's origin: he is a magical clone crafted by the demon Mugen (also called "Infinite") using a fragment of Fract's soul. This act was part of Mugen's scheme to subject Fract to eternal punishment across lifetimes for his atrocities. Aide's existence as a vessel for Fract's soul fragment explains their identical appearance and psychic link.

Confronted with the truth, Aide battles Fract. Their final clash merges their souls, creating a shared consciousness. This fusion forces Fract to experience Aide's memories of suffering inflicted by Bjor's conquests – the first cycle of Mugen's intended eternal retribution. The merged entity departs under Mugen's oversight to face further cycles, leaving Aide's ultimate fate ambiguous.