Become a Hero and a Demon King, and Work Hard to Conquer Myself

Great Magician: "Sir Brave, for the sake of protecting you with my life, defeat the Demon King and save this country!" Demon King: "From today on, you are the Demon King. It doesn't matter if you refuse. I will just take you to play in the guard's amusement park." The brave man and devil who is entrusted with important tasks and forced to do so: Jisei. I embarked on a journey to defeat myself. … A few years later. Companion: "Brave, you should also become a subordinate of the Demon King, otherwise I will kill you. Human power is too weak after all, and I am no longer a human being!" Current Affairs: "Why don't I remember that I have such a subordinate? I have ceased to be a human being!"