Mugen, a powerful demonic entity, orchestrates narrative events to punish the antagonist, Fract, for atrocities committed across multiple existences. He manipulates central characters Aide, Mara, and Dino, exploiting their assassination plot against Fract to reveal their role within his larger scheme of eternal retribution. Explicitly identifying with boundlessness, Mugen declares "I am infinite," reflecting his name's meaning and his nature as an enduring force of supernatural judgment. His interventions ensure Fract faces perpetual consequences beyond a single lifetime, framing the conflict within a cycle of karmic punishment. Operating behind the scenes, Mugen influences key moments to steer outcomes toward his goal of delivering divine justice for suffering caused by Fract's conquests.

As a deity-like figure, his presence underscores themes of cosmic balance and retribution, enforcing divine justice as fate's agent rather than a conventional antagonist. His background and origin remain undefined, emphasizing function over personal history. The character exhibits minimal development, serving primarily as a catalyst for the climax and the story's exploration of morality and consequence. His final act enforces an unending punishment, concluding the narrative with no indication of continued involvement beyond this purpose.