Minami Kaidō, also known as Cure Mermaid, is a main character from the anime Go! Princess Precure. She is a fourteen-year-old second-year student at Noble Academy, where she serves as the student council president. Her elegant appearance, excellent academic performance, and athletic ability have earned her the nickname "the Academy's Princess." Despite her outwardly composed demeanor, Minami possesses a strong sense of responsibility and a caring, gentle nature, often acting as a supportive older sister figure to her friends. However, she can also experience loneliness, and underneath her poised exterior she harbors a desire to become a truly respectable person who can be useful to others.

Minami is the daughter of Tsukasa and Masumi Kaidō and has an older brother named Wataru, with whom she shares a close, affectionate bond; when around him, she reveals a more playful and slightly dependent side. Her personal interests include the sea and drinking tea. Her dream evolves over the course of the story: initially she aims to live up to the high expectations placed on her, but she later realizes the importance of choosing a path that truly makes her happy. This leads her to pursue a career in marine biology, and in the epilogue she has become a marine biologist.

When transformed into Cure Mermaid, the Princess of the Sea, she wields the power of water and ice. She transforms using her Princess Perfume and a Dress Up Key, and her fighting style is elegant and controlled, often employing water-based attacks and her Crystal Princess Rod. As a member of the four Princess Precures, she fights alongside Haruka Haruno as Cure Flora, Kirara Amanogawa as Cure Twinkle, and Towa Akagi as Cure Scarlet. Her key relationship develops with Asuka Kitakaze, a marine biologist who inspires Minami to follow her own dream. Through battles and personal challenges, Minami grows from someone who sometimes suppresses her own feelings to a person who actively pursues her aspirations while supporting her friends with wisdom and warmth.