Rue "Princess Kraehe, Princess Clair, Ruu" Kuroha
About
In all actuality, her other side is Princess Kraehe who is the Raven's daughter. Constantly, she is told that the only people who can love her is her father and the Prince. So, in an effort to gain love and self-worth, she acts out against Princess Tutu. Many times, she makes it more challenging for Ahiru to give back the pieces of Myuuto's heart. Other times, she kidnaps the Prince to lure Ahiru into traps. Her motives are only to gain a sense of worth; regardless, she is not a weak villain and is very much a threat to the rest of the cast.
In the manga:
Rue Kuroha is not the daughter of the Raven. She is just a normal school girl was given a pendant to transform into Princess Kraehe. However, like in the anime, Rue loves Myuuto very much. In the end of the manga, she and Ahiru became friends (and rivals for gaining Myuuto's love).