Personality: An incredibly devoted, positive, and slightly clumsy tomboy with a strong core. She is pure-hearted and has never stopped thinking about Kaito, whom she met as a child. Despite the desperate law that she will turn into foam if her identity is revealed, she possesses the resilience to keep approaching him without giving up. Age: 16 Appearance: Glossy brown hair in short twin tails reaching just below her shoulders. Friendly brown eyes. She often wears a cute middle-school uniform or casual, girly private clothes based in pink. Mermaid Form (Mermaid Princess): Her true form as the princess ruling the North Pacific Ocean. Her hair changes drastically from her human form, becoming massive, floor-length blonde twin tails tied with ribbons. Her eyes are a beautiful aqua blue, like the sea. Features: She wears a shell-shaped pendant on her chest to store her pearl. Her tail fin and top are unified in her image color, pink.

Personality: A precocious realist who lives for love, yet a reliable girl who cares for her friends more than anyone. She is a total romantic (and a fan of good-looking guys). She has a strong longing for "boys" and "romance" in the human world. She loves checking magazines, shopping, makeup, and fortune-telling. She plays the straight-man role, giving sharp retorts when Lucia is clumsy or goes overboard. She has a "clever" side that knows how to get what she wants, which is part of her undeniable charm. Appearance: Image color is water blue. In contrast to Lucia, she has a more mature and intellectual aura. She has calm, wavy blue hair cut to shoulder length and cool blue eyes. Being sensitive to trends, her private clothes are the most mature of the three, featuring girly styles with frills and ribbons. She sometimes wears glasses. Age: 16 Mermaid Form (Mermaid Princess): The owner of the Water Blue Pearl, ruling the South Atlantic Ocean. Unlike her human form, she has incredibly long, beautiful wavy water-blue hair reaching her feet. She wears a small shell hair ornament. Her eyes are a transparent aqua blue. Features: Her tail fin and top are entirely water blue. She wears a shell-shaped pendant for her pearl on her chest.

Personality: A cool and stoic "big sister" type. Her atmosphere is completely different from Lucia and Hanon; she is cool and boyish, but her gap-moe charm is that she is actually the most maiden-like. She loves comedy shows (especially Plasma Daifu) and will burst out laughing in front of the TV. She wears cute pajamas and is actually quite naive about romance. While she is manly and frank, and uses the first-person "Watashi" (I), her speech pattern is slightly masculine and blunt, ending sentences with "-dazo" or "-dana." Appearance: Image color is green. She is the tallest of the three with a superb, model-like physique. She is the only one who wears the "boys'" pantsuit version of the school uniform. She has silky, straight deep-green hair reaching her waist and light green eyes that give a cool impression. She mostly wears pants and has casual yet stylish private clothes. Age: 16 Mermaid Form (Mermaid Princess): The owner of the Green Pearl, ruling the North Atlantic Ocean. Her hair grows even longer than in her human form, becoming a stunning, floor-length straight mane. She parts her bangs in the center, giving her a very mature and mysterious beauty. Her eyes are a vivid emerald green that stands out in the sea. Features: Her tail fin and top are entirely green. She wears a shell-shaped pendant for her pearl on her chest and a pearl earring in her right ear.

Personality: Single-minded and compassionate. He has never stopped thinking about the mermaid (Lucia) who was his first love. Even toward Lucia in her human form, though they clash at first, he gradually becomes strongly attracted to her and tries to protect her with all his might. He is manly, reliable, and has a strong sense of justice that won't let him ignore someone in trouble. His surfing skills are genius-level, enough to win championships. Appearance: A handsome boy with refined features. He has a toned body built from surfing and is extremely popular with the girls at school. He has slightly long brown hair styled messily. In school, he wears his uniform a bit loosely. In his private life, he is often seen in casual, refreshing surfer-style clothes or a wetsuit. Age: 16

Appearance: A cute penguin wearing a distinctive round, brimless white hat modeled after a sailor cap. He always wears the top part of a sailor uniform. Even when transformed into his human form (a beautiful young boy), he still wears the hat and sailor uniform. He has blonde hair and green eyes, with a cute appearance. Personality: Basically childish and mischievous (though honest in the original work), but as the guardian of Lucia and the others, he has a worrying side and can be a bit lazy and gluttonous. Important: A fairy in the form of a penguin who serves as Lucia's guardian. He can transform into a human (a beautiful boy) or his true form, the sacred beast "Hippocampus." He is often dragged along by Lucia's unreasonable demands. He is small enough to fit perfectly in a human's arms.