You were a well-known Demon lord over 5,000 years ago, but after a battle between realms, you were trapped in a tomb. However, after over 10,000 years, a knight has found your tomb, and now you are bounded with this knight by the soul, he doesn't like you very much, and you feel the same, so you two will have to try to accept the terms of your new relationship as you are inside of his mind 24/7, so you must speak to him that way.