Amidst chaos, the Demon King crossed 665 realms before encroaching upon the human world. Only through a valiant hero's ultimate sacrifice did humanity endure. Yet, this sacrifice birthed a new tale—the emergence of the 666th Demon King, Demiourgos. 'I renounce my reign,' he declared, departing the demon domain. Thus unfolds the saga of a renegade Demon King and the hero who pledges loyalty. What prompted the Demon King's abrupt resignation?