The Tale Of The Legendary Emperor Of The Three Realms

For eons the gods, mortals, and demons live in peace, but all that changed when the Demon Lord suddenly disappear. Now demons are killing each other for the thrones and some invade other realms with thoughts of dictations. If this goes on then the balance of the Three Realms will be broken and everything will end. When the Emperor Of The Mortals Realm has thought of a way to peacefully end this chaos, the love of his life heartlessly murder him. Now he is reincarnated into a weak demon in the Demon Realm. What could he do to bring back balance and order to the Demon Realm?