The haughty mermaid princess of the Seahorse Realm. Bold and brimming with confidence, Red Ruby believes she is the most stunning of the seven princesses. She considers herself beautiful, stylish, and elegant, claiming to be incredibly popular on land as well. She doesn't care if people call her a 'princess complex' case—after all, she really is a princess! She expects everyone to look forward to her becoming the next queen.

The indecisive and aegyo-filled mermaid princess of the Sea Anemone Realm. Lovely and cute, Orange is also a talented cook. She often offers her homemade cookies to others. She shares a secret that her mother calls her the 'cutest and sweetest cookie in the world,' and she firmly believes her mother is always right. She enjoys being adored by everyone.

The shy mermaid princess of the Shell Realm. Finding it difficult to speak her mind, Yellow Gold prefers to express herself through drawings. She is quiet and easily embarrassed, which makes her feel a bit lonely as she lacks friends. Though she finds it hard to initiate conversations, she finds comfort in art, even if she struggles with social interactions.

The intelligent, model student mermaid princess of the Stingray Realm. Ranked first in the whole school, Green Leaf enjoys the undivided attention of her teachers. She attributes her intelligence to reading many books and doesn't see her confidence as bragging—she simply feels she knows more than the others.

The competitive mermaid princess of the Jellyfish Realm. An all-around sports girl, Blue claims no one can beat her in speed. Having grown up among brothers, she is sometimes called insensitive, but she insists she never has bad intentions and asks others to just be cool about it.

The lonely outsider mermaid princess of the Deep Sea Realm. A girl of many secrets, Indigo is aware of the strange rumors surrounding her due to her solitary and blunt nature. While she can't reveal everything, she wants people to know that her true self is very different from the rumors.

The tomboyish mermaid princess of the Starfish Realm. A free spirit, Purple's strengths are her energy and cheerfulness. Driven by curiosity, she has to experience everything firsthand. Although she can be impulsive and a bit reckless at times, she promises not to cross the line.

A mysterious mermaid prince searching for his lost homeland. A school senior, Grey specializes in deciphering ancient scripts, which allows him to find new transformation spells. He spends his time reading history books and old records. He acknowledges that he might seem suspicious, but claims he just has many secrets and hopes to share his true story someday.