My take on Urashima Taro is a bit more direct in its interpretation (versus what I chose to do for The Bird Maiden). I wanted to portray the princess of being more closely incorporated with the sea itself. After all, our main character is a fisherman in a time when the occupation itself saw a lot more peril. It would not be unusual for the sea to be treated as a character or entity of its own in folklore. Also, who doesn't want to be guided out of certain death by a giant woman?
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On The Bird Maiden:
At a human level, versions of the story often deal with the lot of a young woman who, far from home, has been trapped into a union through the strength and guile of a stranger. There is a kind of demand for the wife to be both bird (for this is what makes her otherwordly), and woman (which positions her as a potential wife). Migratory and trapped. That is her nature and fate - to be both and neither.
There are variations of the story in East Asia (varying origins) where the husband/father is taken to heaven, sometimes able to return to earth by gaining "heavenly favor". Sometimes not.
But there is almost always the inclusion of the bird-maiden regaining her robes and returning back to her home in one way or another.
Cranes are often employed as a motif of a symbolic link between heaven and earth, so perhaps the stories can not just be interpreted as a literal taking of the bird-maiden as a wife - but of a man's meddling with matters of life and death. If you were the bird-maiden, stripped of your wings, forced to wed the person who stole them, and who kept you tethered to earth...would you just accept fate? I like to think that sometimes she doesn't.