Ahiru Arima, also known as Duck in English, is the protagonist of the series. She is a friendly, kind-hearted duck who was given a magic pendant that turns her into a human girl. This pendant also allows Ahiru to turn into her alter-ego Princess Tutu.
Ahiru is a friendly, kind-hearted, and goofy character. Like a duck, she is easily excitable, clumsy, and talkative. She can be extremely scatterbrained and uncollected when nervous. As time goes on, she gains a strong determination and is more willing to take risks for her friends.