Three months have passed since the Demon King was defeated by a hero. Mankind rejoices over their victory, but dwellers of the demon world do not share the same sentiment. With the loss of their king, they must now hold a tournament to decide who will become his successor.

Monitoring the competition is the hot-headed yet powerful Vamirio—one of the Four Heavenly Kings. Among all the participants, she is extremely distrustful of one: Helck, a human hero who claims to hate humanity. As much as she wants to get rid of him, it is impossible due to Helck's incredible strength and popularity.

Amidst the competition, Vamirio discovers that humans have vanished from various towns. As a result of this puzzling turn of events, Vamirio grows desperate to reveal Helck's true intentions by carefully crafting a plan to make Helck lose. If she proves to be successful, she might uncover where his loyalty truly lies before the demon world is endangered.