Black Clover: Secre Swallowtail

Secre Swallowtail is the servant of Lemiel Silvamillion Clover, prince of the Clover Kingdom and the first Magic Emperor. She is transformed into an anti-bird named Nero after sealing Lemiel into a statue. Five centuries later, she decides to stay alongside Asta after encountering him at the beginning of the Magic Knights Entrance Exam, and is later accepted herself as a member of the Black Bull squad of the Magic Knights.