Nyah fell in love with a mortal man named Harold, but Harold was already married to Sandy. Nyah swam with Harold under the sea, and promised him the eternity with her, if he'd leave his wife and would come with her during the next tide. Mr. Roarke tried to warn Nyah away from Harold, but Nyah felt too strongly about her love and ignored his warning. After thinking it over, Harold left his wife to be with Nyah, but Sandy stopped him saying that she still loves him. Sandy went as far as to attack Nyah, but Nyah being a mermaid got the upper hand in the sea and pushed her under the water. Harold stopped Nyah from killing Sandy, and returned with his wife to the dry land leaving Nyah alone again.
Later Nyah Returned, but now she didn't want to lure men into sea, she wanted to find love on the dry land herself. She let Mr. Roarke to give her legs, so she could find love of the Fantasy Island. Nyah constantly got in trouble and once she even got spanked by Mr. Roarke. She eventually thought she's in-love with Mr. Roarke, but Roarke set her strait, that it's mostly parental love. Nyah let herself to be turned back to mermaid to save Tattoo, who she sent on the sea and made a storm to hold her there.
After several years Nyah again returned to Fantasy Island wanting to become mortal. But when Mr. Roarke refused her wish, she wanted revenge on him.