Princess Tutu

Ahiru "Princess Tutu"

Ahiru (which translates to duck in Japanese) is in all reality, a duck herself; however, in the beginning of the series she was turned into a human girl by Drosselmeyer. He also bestowed upon her a pendent which causes Ahiru to transform into her other-self, Princess Tutu. This was all caused by her desire to see Mytho, the Prince of the story, to smile. It turns out her role as Princess Tutu is to gather Mytho's missing heart so he can gain back the many feelings of sadness & happiness.

It is apparent from the start that Ahiru, her as a human, duck, and Princess is feverishly in love with the Prince. Regardless, if she confesses her feeling to him she will vanish (or so the story goes). As such, she is stuck in this awful predicament, but she always willingly goes to fetch Mytho's heart to aide her beloved, lifeless Prince.