Ryuusei Narukami spends his days shut in his apartment playing games, a NEET with no idea his quiet second life is about to end: he was once a demon king in another world, and Meteor Hanaori, the hero who struck him down, has been reborn as a high school girl and turns up at his door. Determined to rejoin society, Ryuusei takes a teaching job and lands at Meteor's school, where an old rivalry has to share space with homeroom, and neither of them can quite let the fight go.