The Glendales of the Black Emperor

The Demon King who ruled the Demon Realm, Raymond, was defeated in battle by the "Hero" Lia. But Lia spared his life, sealed his demonic power, and then vanished without a trace. Left alone in the forest, Raymond encountered a silver-haired girl named Lia being chased by a giant beast. Thus began the Demon King's great campaign in the human world!