Onio to Houkou Hanayome no Himegoto

"Become my nighttime attendant." Tsuzuku is reincarnated into the world of his favorite book, where he works as a servant at the lowest level in the mansion of the villainous demon, Koyomi. He lives in extreme poverty, oppressed daily by the wife who controls the mansion. One day, Tsuzuku hears a rumor that Koyomi is preying on waiters, and is suddenly appointed as one of them...!? "Is Koyomi really doing such terrible things...?" Tsuzuku goes to find out the truth, only to find that Koyomi has completely changed. The story of a secret master-servant relationship between a kind-hearted, terrifying demon and a waiter with special powers begins!! https://www.cmoa.jp/title/318448/