Mitsuki Kouyama (高山 満月 kōuyamā mitsūkī) is a 12 year old girl and she wants to be a singer, but because her throat got her a pain. and Mitsuki wants to transform to become a 16 year old and so she sing for her feelings. And her childhood friend eichi to make her own promises. And she give her feelings with the angel's feather become the moon mermaid princess given by aqua regina.
- Mitsuki can joins the group of the mermaid princess in Power Rangers Data Squad by the episode The Mermaid Princess Rescue and she is given by goddess aqua regina.
- Mitsuki's theme color is yellow-green and her sub color is light pink.
- Mitsuki will appear in Adventure of the Jewel Kingdom from Power Rangers Harmony Force by the episode, and she will be revealed by The Moon Mermaid Princess.