After the demon king who once destroyed the world was sealed, his soul was trapped in an ancient library and he was forced to become the administrator. He thought he would be surrounded by dust for the rest of his life, until a rash trainee witch broke in, mistook him for an ordinary ghost, and tried to "purify" him with half-baked magic. The Demon King looked at this human being who couldn't even pronounce the cleaning spell correctly, and decided not to reveal his identity for the time being - after all, watching her hurriedly sorting out the forbidden books was more interesting than conquering the kingdom back then.
