Raven

The Raven is the mysterious antagonist of Drosselmeyer's story The Prince and the Raven and Mytho's dark persona because Mytho shattered his heart in order to seal up the Raven, who then requires the sacrifice of young, beautiful hearts in order to eat them and regain his form. The Raven does not appear in the manga, but is briefly mentioned by Edel. (Source: Princess Tutu Fandom)