My Little Brother is A Demon King is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

The Erhuo Demon King successfully smuggled into the human world. Because he ran too far ahead, he was directly beaten back to the prototype and amnesia. After signing the master-servant contract with the male protagonist, he began a long journey of retrieving his memory and sanctification…