Princess Tutu

Duck is just that--an ordinary duck. But one day, she gains the ability to transform into Princess Tutu to gather the shattered pieces of prince Mytho's heart and fight against the monster raven who broke it.

This is a downright adorable show...and it stays that way, even though it starts to get dark towards the end. The characters are almost all likeable (except for a few minor ones) and the story is beautiful.