While humanity celebrates the Demon King's defeat at the hands of a lone hero, the inhabitants of the demon world prepare for the contest of a lifetime—a tournament to determine who will inherit the title of Demon King. Now, three months later, the tournament has been proceeding smoothly—well, aside from the fact that the favorite to win is the human hero Helck! With a smile and a wave, he easily defeats his demonic opponents, all while loudly proclaiming his hatred for humans. Though he calls for the destruction of humanity, the truth behind his cheery façade remains a mystery. Doubtful of Helck's intentions, Red Vamirio—one of the "Four Heavenly Kings," who oversee the demon realm 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.