After the Demon King's defeat by a hero, humanity celebrates, but the demon realm faces turmoil as a successor must be chosen through a tournament. The fiery and formidable Vamirio, one of the Four Heavenly Kings, closely watches the competition, particularly wary of Helck, a human hero with a disdain for his own kind. Despite her desire to eliminate him, Helck's strength and popularity thwart her plans. As Vamirio investigates the mysterious disappearances of humans in various towns, she becomes determined to expose Helck's motives by devising a scheme to defeat him. Her success could unveil where his loyalties truly lie and safeguard the demon world from impending peril.