In Princess Tutu, Ahriu is given a pendant that detects pieces of the prince's heart, and allows her to turn into Princess Tutu so she can return them to him.
In the penultimate episode,
Ahiru tries to avoid giving Mytho the last piece of his heart, because it's actually the gem she's been using to turn into Princess Tutu - and without it, she'd revert to her true original form, a duck.
But I don't recall it being stated just what that piece of heart was. I thought it might be Love, but that was in Akt 11 La Sylphide. Wikipedia and the rest of the Princess Tutu wikia doesn't say, so does anyone know which emotion turned Ahiru into Princess Tutu?
Bonus points if you also know what the shards from the five gates to the town were.