This is the story of a former Demon Lord, once the most powerful in another world, who once again reigns supreme on Earth. Ten years have passed since dungeons first appeared on Earth. Humanity has gained superhuman abilities known as "Levels," "Stats," and "Skills," and those who use these powers to conquer dungeons are called Seekers. The protagonist, Renya Kamikura, suffers from recurring strange dreams and headaches, until one day, he remembers his past life as the mighty Demon Lord of another world. To his shock, all the dungeons appearing on Earth are ones he had created during his time as the Demon Lord! With his exceptional skills, extensive battle experience, and deep knowledge of magic and dungeons, Renya quickly ascends to become the strongest on Earth, standing unrivaled against all formidable opponents.