In the distant past, a war between humans and demons brought about widespread chaos. To put an end to this conflict, Demon King Anos Voldigoad willingly sacrificed his life, hoping to be reborn in a peaceful future. In preparation for their king's return, the demon race created the Demon King Academy, an elite institution tasked with determining Anos' identity when he reawakens. He reincarnates two millennia later, but to his surprise, he soon learns that the level of magic in the world has drastically waned during his absence. Moreover, when he enrolls at the academy to reclaim his rightful title, he finds out that demonkind remembers him differently. This "lack" of common knowledge renders him the academy's outlier—a misfit never before seen in history. Despite these drawbacks, Anos remains unfazed. As he sets out to uncover those altering his glorious past, he takes it upon himself to make his descendants recognize that their ruler has finally returned.

As peace returns to the demon realm, Anos Voldigoad wishes nothing more than to put his reputation as the Demon King of Tyranny to rest and go back to being a misfit at the prestigious Demon King Academy. Unfortunately, any tranquility is fleeting: sinister demons, kings, and deities plot Anos's demise from the shadows. Rumors spread about the "Child of God," a being whose power may rival that of Anos. To uncover the truth and eliminate the potential threat, Anos must journey deep into the land of spirits. However, the spirit world is shrouded in mystery, and it may only be entered after undergoing a series of difficult trials. With unrivaled power and confidence, Anos braces himself to defeat various formidable enemies with grandiose titles. But he—with the assistance of his trusted allies—will barely have to break a sweat as the true Demon King of Tyranny.