B is for the Bird Princess

Today's princess is brought to you from Thailand (although the story is known in other Southeast Asian countries as well).

Her name is Manohara, and she is a Kinnari: half bird, half human (lower half swan, as shown in the picture). She is not just any Kinnari either, she is the youngest of the seven daughters of the King of the Kinnara. She lives in the mythical forest Himavanta together with many other amazing creatures of the mythology of South-East Asia.

(Before we go any further with this it bears mentioning that Kinnari can transform themselves into a fully human form as well, which probably makes them marrying humans a lot less awkward)

Manohara wears a precious gem on her forehead that gives full control over her to whoever holds it. This becomes important as soon as a hunter called Halaka lassoes her and drags her out of the lake where she was taking a bath.
(The magic lasso has a whole fascinating story behind it, by the way)
The hunter proceeds to hand the swan-girl over to a prince called Sudhana, who promptly falls in love with his captive (but not enough to give her back the jewel). Manohara returns the feelings and becomes his wife.

In the second part of the story the prince goes away to war and the Kinnari's jewel is handed over to the queen mother. When some advisors in court start scheming to have Manohara sacrificed for the success of the war, the queen finally hands her jewel back and lets her escape. Manohara leaves clues along the way for her husband, and then flies home, and spends her time "trying to wash the human smell off."

Of course the prince eventually finds her, following the clues. He is a hero, after all. 

You can read the full story here as depicted on the reliefs of the temple of Borobudur in Java.

This story belongs to a folktale type known in most parts of the world, called AT 400 - The Swan Maidens. You can find several other versions listed here and here. In China a similar story is the basis of a yearly festival.
This tale type usually includes a male hero catching a bride when she sheds her animal form (usually a bird, sometimes a seal - these are called selkie stories). There is always something that gives the man power over the supernatural bride: it is usually the shed skin or feathers, or sometimes a robe or a veil. In this case, it is a jewel (since Manohara does not shed her feathers to swim in a lake, which leads to her being lassoed around the neck instead of just having her skin stolen, ain't it nice?) Usually the bride finds this hidden item later, after having children, reclaims it, and returns to her own home, leaving the husband and the bunch of half-human babies behind.
It is a woman's tale, and rarely ever has a truly happy ending. Even in Manohara's case the means of her becoming the prince's wife are more than questionable and scream Stockholm syndrome. But let's not forget, this story was born in another time, and another place.