Reincarnation M: Sorcery Fight

Meant to save the world but accidentally got reincarnated as the Demon King?! Should you travel time and space to save the world, but unexpectedly you reincarnated as the Demon King who always ends up being eliminated by the brave warrior! "I don't want to die yet!", you shouted deep inside. "I can't eliminate myself, can I?", you had no choice but to hide your identity.