In a world where heroes protect the people and villains threaten society, those with supernatural abilities live their lives using their powers for one side or the other. Rou Koyanagi and Guest were once classmates at an academy for aspiring heroes. They underwent the same training, completed missions together, and shared ordinary daily lives. Since those days, Rou harbored secret feelings for Guest, though he never found the words to express them. Following a certain incident, Guest abandoned the path of a hero and became a villain. Now, Rou has become a hero—a swordsman who rends demons and slays spirits. Meanwhile, Guest is one of the villains he is tasked to hunt. The person who was once his closest companion is now the enemy he must point his blade toward. Yet, Rou cannot bring himself to see Guest as just another villain.