One night, a boy finally gathers the courage to confess his love to his crush, Yua. Before he can speak, a meteor strikes him dead, and he is reborn in a fantasy world. After briefly accepting his fate as an inhabitant of this new realm, he defeats the Demon King in mere seconds. Using the hacking skills he acquired as a hero, he finds a way to return to his original world to complete his confession. Back in his classroom, he discovers that every single one of his classmates has also returned from being heroes in various other worlds. Then he sees Yua. To his shock, the girl he likes is not a returned hero at all. She is the reincarnated Demon King he slayed in that other world.

The story is set in a modern-day Japanese high school classroom that has become an unexpected meeting point for dozens of interdimensional veterans. The protagonist is a boy defined by his determination to confess his feelings, a mission that drove him to slay a demon king and hack reality itself just to get back home. Yua, the object of his affection, is the reincarnation of the very demon lord he effortlessly destroyed, creating an impossible romantic complication.

The early narrative focuses on the protagonist's failed confession and his immediate, violent isekai detour. After his swift return, the plot centers on the chaotic classroom dynamic where former heroes from countless parallel worlds now coexist. This tense peace is shattered by the central revelation that the demon king lives on as his crush. Subsequent arcs explore the protagonist trying to navigate a normal school romance with someone who, in a past life, was his mortal enemy, all while his classmates possess the powers of legendary heroes and remain unaware of Yua's true identity.