Ondina is a talented, confident mermaid who is determined to save Mako Island from the land boy Zac, who transformed into a merman. She can be reckless and wilful, and has a problem listening to anyone who doesn’t agree with her. Although stubborn and single-minded, Ondina is also fiercely loyal to her friends, especially her best friend Mimmi. Ondina has a soft side, as seen in her relationship with the merman Erik, which forces her to rethink her prejudices against his kind.