The ages-old battle between good and evil takes an unexpected turn when the Demon Lord, a being capable of destroying the entire world, suddenly announces he wants to call it quits. Rather than pursuing his destructive ambitions, he becomes fascinated by humanity and makes an unusual request to his longtime rival, the hero girl Asuka Kagurazaka: he wants to live with her to study human behavior up close, offering a global truce in exchange for becoming her roommate.

What follows is an improbable slice-of-life comedy that blends action sequences with absurd everyday situations. Asuka, a seasoned monster fighter, finds herself navigating the bizarre logistics of cohabitating with her former nemesis. The Demon Lord, despite his world-ending power, approaches ordinary human experiences with the curiosity of an otherworldly being, leading to humorous clashes and unexpected moments of connection. The series establishes a dynamic where sworn enemies shed their traditional tropes to pursue something resembling a normal life.

The story builds toward a significant turning point with the appearance of the crimson moon, a celestial sign that has long foretold an impending apocalypse. When Asuka confronts the Demon Lord beneath this ominous sky, she discovers her own secret power: her mere presence neutralizes his magic entirely. The crimson moon instantly reverts to its normal color, revealing that Asuka unknowingly possesses the ability to maintain balance in the world simply by being near him.

This revelation reframes their entire cohabitation arrangement. Both characters recognize that Asuka must remain by the Demon Lords side to prevent disaster, providing a logical and somewhat ironic justification for their continued proximity. The series concludes with this understanding firmly in place, closing its main narrative arc in a way that returns to the established status quo while affirming the necessity of their unusual partnership for the worlds survival.