A young man named Yuma is summoned to another world, where he succeeds as a hero and defeats the demon lord. After completing his quest, he manages to return to his original world and resume his normal life. However, he accidentally brings the demon lord back with him. Now Yuma must navigate high school life while dealing with the unexpected and chaotic presence of the demon lord in the modern world.

The story is a comedic boys love narrative that follows Yuma and the demon lord as they try to adjust to their bizarre living situation. Yuma is a high school student who previously experienced an isekai adventure, while the demon lord retains his full personality and power from the fantasy realm. The plot revolves around their attempts to find a way to send the demon lord back, though their efforts are complicated by the demon lords uncooperative and mischievous nature. As they spend more time together in mundane settings like school and everyday life, an unconscious romantic tension begins to develop between them, with both characters slowly becoming aware of their changing feelings.

The setting alternates between the modern Japanese high school environment and references to the fantasy world where Yuma originally fought as a hero. The narrative progresses through comedic episodes centered on the demons lord's inability to understand or adapt to human society, leading to various misunderstandings and humorous situations. A notable story arc involves the demon lord developing an unexpected taste for human food and becoming fixated on a particular classmate named Satou, which creates additional complications for Yuma. The manga builds toward the pair navigating their unspoken romantic attraction while trying to resolve the supernatural problem that binds them together.