She begins by being in a relationship with Mytho, but as her relationship becomes threatened she transforms into Princess Kraehe in order to thwart Princess Tutu.
Rue is a very difficult character to read. When the tale begins, she is in a relationship with Mytho "just because" more than anything else, yet once Mytho is threatened from being taken away from her by gaining his heart, she finds that she does indeed care. As her feelings are revealed to herself, and Mytho is pulled farther and farther away from her into Princess Tutu's arms another side of her appears.
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 Mytho'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.