Lucia is one of the 7 mermaid princesses, who resides in the North Pacific Ocean. She holds the pink mermaid's tear, which unfortunately is lost...

When Lucia was little, she ventured out onto the sea surface one night, and encountered a fireworks celebration on a cruiseship! Joining in the festive spirit, she sang a song with a mermaid's beautiful voice. A little boy was attracted to her voice and comments on how pretty it sounds, and Lucia is delighted! He then asks her why is she in the ocean, so Lucia revealed her identity by showing him her tail. The boy was absolutely surprised that he has seen a real mermaid!

Interrupting the brewing romance, a giant wave crashed onto the ship, and the boy fell into the icy ocean! Lucia quickly went after him. He was on the verge of death when she finally got him onshore. To save him, Lucia used the powers of her Mermaid's Tears (which looks like a pink pearl). The boy kept the pearl ever since.

Therefore it's up to Lucia to retrieve her pearl back. With her adorable guardian penguin, Hippo, she disguises herself as a human girl named Nanami Lucia in order to search for the boy. While onland, she meets a surfer-dude named Kaito, who looks awful lot like the boy who has her pearl...nah, couldn't be. The boy isn't a ruthless womanizer like Kaito!

Meanwhile, a clan of evil sea monsters are on the lookout for the 7 Mermaid's Tears as well. During a surfing competition, a monster detects that Kaito has one of them, and pulls him underwater to get it. Of course Lucia can't let Kaito die, she quickly jumps into the water to battle the monster (which turns her back into her mermaid self). When a semi-conscious Kaito sees his beloved mermaid in trouble fighting, he throws the pearl to Lucia, which transforms her into a singing Magical Girl named "Pink Pearl Voice"! She is then able to defeat the monster by singing her childhood song, using her magical microphone.

Lucia is finally reunited with her first love, Kaito...the thing is, he doesn't know her name, nor he knows that she is his classmate, Nanami Lucia. He only has the mermaid in his mind. Moreover, she cannot confess her love to Kaito (in both human or mermaid form), because she will turn into bubbles immediately. But if he realizes her love on his own, all will be fine.

How will Lucia tell him indirectly that she really is the mermaid he thinks about day and night? And as one of the three blessed mermaid princesses, how will she defeat the sea monster clan, who has begun to destroy the mermaid kingdom in order to capture all seven mermaid princess? This would be the main plot of this uber-cute mahou shoujo anime