Ryusei Narukami spends his days as a shut-in NEET, holed up in his apartment and immersed in video games. What no one knows is that in a previous life, he was the fearsome Demon King of another world. His quiet, isolated existence is shattered when a high school girl named Meteor Hanaori suddenly appears at his door. She is the reincarnation of the Hero who once defeated him, now living as an ordinary teenager in the modern era.

This unexpected reunion motivates Ryusei to reintegrate into society. He lands a job as a teacher at Mikenshi Girls High School, only to discover that it is the very school Meteor attends. Reborn into a peaceful world without any grand quest or apocalyptic battle, the former Demon King and the former Hero must navigate an entirely new kind of conflict: high school life.

The narrative is a romantic comedy that focuses on the awkward and playful dynamic between the two leads. Ryusei must balance his new professional responsibilities as a teacher with his past identity, while Meteor, whose name reflects her explosive personality, struggles to contain her combative instincts from their past life. Their relationship evolves from that of reincarnated rivals to a developing romance, complicated further by the student-teacher setting. As the series progresses, they eventually begin dating and later move in together, exploring how two people destined to be enemies can build a life in a world that no longer needs a hero or a demon king. The story takes place in a contemporary Japanese city, centered around Mikenshi Girls High School, a setting that forces the former fantasy adversaries into mundane yet awkwardly intimate situations like homeroom, school festivals, and faculty meetings.