Danterio, the “kind Demon King” who once saved the world from an angelic invasion, fights a final battle and then loses consciousness. When he next opens his eyes, he finds himself 600 years in the future—in modern Japan—reborn in the body of a young man named Daiya Mizukami, who died from bullying and an overdose of magic‑enhancing drugs. Learning of Daiya’s bitter regrets, the Demon King first deals with the problem right in front of him: he crushes the bullies who drove Daiya to his death in an instant. But when he looks at the wider world, he discovers that magic has weakened, and the angels he once defeated have begun to move again. “I am the Demon King, Danterio. I will teach you… how to kill angels.” Thus begins a modern battle‑action story where the strongest Demon King rampages through contemporary Japan, combining reincarnation, school life, and brutal angel‑slaying action.