A series of mysterious disappearances plagues the city, and rumors swirl that the missing have been reincarnated into another world. High school student Yoshimichi dismisses the gossip as nonsense—until his childhood friend Yuma vanishes without a trace. His eccentric classmate Otogi, convinced that Yuma was spirited away by reincarnation, declares her own desire to go to another world and drags a reluctant Yoshimichi into a suspicious building. There, the two are forcibly transported to a fantasy realm.

Upon arrival, Yoshimichi discovers that his body now houses the soul of a Demon King. This possession grants him immense latent power, but it also marks him as a target in a world where the traditional roles of heroes and demons have been reversed. The fantasy realm has been overrun by transplanted “heroes” from Earth, who abuse their abilities and have corrupted the order of the land, turning it into a place of tyranny and exploitation. Rather than a righteous savior, Yoshimichi finds himself aligned with the demonic force inside him, forced to navigate a society where the line between good and evil is blurred.

The narrative follows Yoshimichi as he comes to terms with his new power and the demon king’s influence, while Otogi pursues her own isekai ambitions. Together they confront the heroes’ oppression, uncover the truth behind the mass disappearances, and grapple with what it means to wield demonic strength in a world that has lost its moral compass. The story blends action and dark fantasy with a satirical twist on the classic isekai formula, centering on a protagonist who is neither a chosen hero nor a simple victim, but an unwilling vessel for the very evil the world fears.