In the real Hans Christian Andersen story written 150 years ago in Denmark, (in this edition illustrated amazingly by Charles Santore, I especially love the hair), the mermaids did not have souls. Mermaids live for hundreds of years, but then die without immortality as humans did. The story is not just a quest for love, but for a soul. If the Prince falls in love with her, she also gains a soul and life after death. When she trades in her voice to the evil sea witch (a hideous creature) for legs, she also suffers excruciating pain when she uses them.
Illustrations for the original Little Mermaid by Charles Santore. Ariel consults with the sea witch.
When she finds the prince and his court, she cannot speak, but her eyes communicate her heart. Also at one point she dances "as noone has ever danced before". The Prince and he become friends, but in the end he falls for another woman. Ironically, if he had known who saved him, he wanted only that person, but she could never speak to tell him. Upon his wedding day, she would instead die, as per her bargain with the sea witch-- changed into foam upon the sea. As the dawn of the morning light comes, and her death, her sisters arrive. They had cut off their hair and given it to the witch to allow her to return into mermaid form and live out her life. But she actually refuses, so sorrowful is she to see the person she loves with another that she gives in to death-- but there is reprieve. The sun looks down kindly upon her so she doesn't feel the pain of death- and she turns into an angel.
"She saw the bright sun, and above were floating hundreds of transparent, beautiful creatures. She could still catch a glimpse of the ship's white sails, and of the red clouds in the sky, across the swarms of these lovely beings. Their language was melody, but too ethereal to be heard by human ears, just as no human eye can discern their forms. Though they had no wings, their lightness poised them in the air. The little mermaid saw that she had a body like theirs, which kept rising higher and higher from out of the foam.
'Where am I?' she asked, and her voice sounded like that of her companions--so ethereal that no earthly music could give an adequate idea of its sweetness.
'Among the daughters of the air!..."