It was an era when humanity emerged victorious from the great war among the five races vying for supremacy on the surface. However, that world was suddenly "overwritten" before the eyes of a boy named Kai.
In a world resembling a parallel universe, Kai witnessed a scene where history had been tampered with, and humanity had lost the great war — a world where dragons and demons ruled the surface, and furthermore, Kai had become a forgotten existence to all humans.
But upon meeting the mysterious girl Rinne, Kai inherits the sword of a hero and challenges the mighty enemy races that reign in this world without heroes.
A boy forgotten by the world sets out to "reclaim the true world" — the curtain rises on a classic fantasy battle!