A brief description of the manga Level 0 Demon King Becomes a Adventurer in Another World:
Meet the Evil King Valt, ruler of This Continent of Darkness.
After being conquered by a set of heroes, he had been reborn as a person, with his abilities intact!
“I will start within this world. And now the entire world will soon be mine!”
Valt grabbed the attention of this elite adventurer Iris. With Iris because his defender, he glanced in the Royal Adventurer Training School and promptly surpasses his seniors along with his unnatural power! He proceeds to use his abilities as an Evil King to good effect, dominating the new world that he finds himself …