Unlike the original Hans Christian Anderson story, Disney’s 1989 animated movie The Little Mermaid appears to be a Girls Underground story, of the sort I call “reverse” (where the girl starts off in an “otherworld” and comes to our world).
Ariel, 16, is a mermaid dissatisfied with her life in the ocean, who wants to live in the human world. On an excursion to the surface, Ariel saves a prince from drowning and falls in love with him. Desperate to join him, she makes a deal with the sea witch Ursula to become human for three days, in exchange for her voice. She must find true love with the prince in that time, or she will stay a mermaid forever and be at the mercy of her adversary.
While Ariel tries to get the magic kiss from her prince, Ursula disguises herself as a woman and, using Ariel’s voice and some magic, captures the prince’s heart and they are to be married immediately. Ariel’s companions disrupt the wedding and expose Ursula’s fraud. Too late, however, and Ariel is turned back into a mermaid, kidnapped by the thwarted Ursula, and used as a bargaining chip to steal her father’s kingdom.
Ariel has a confrontation with her adversary, although it is actually the prince who defeats her (typical Disney). And of course, her father decides to make Ariel human forever, and she can marry her prince, and everyone lives happily ever after – unlike the original story in every way.