While humanity celebrates the defeat of the Demon King by the hands of a lone hero, the denizens of the demon world prepare for the contest of a lifetime—a tournament to decide who would inherit the title of Demon King.

Now, three months later, the tournament has been proceeding smoothly—well, other than the fact that the favorite to come out on top is the human hero Helck! With a smile and a wave, he easily bests his demonic competition, all while loudly proclaiming his hatred for humans. Though he calls for the destruction of humanity, the truth of what lies behind his cheery façade remains a mystery.

Doubtful of Helck's intentions, Red Vamirio—one of the "Four Heavenly Kings," who oversee the realm of the demons together—seeks to uncover what the hero is truly after. With the title of "Demon King" at stake, the fate of the demon world rests on her shoulders.