Mermaid Melody Pichi Pichi Pitch.

Lucia, Mermaid Princess of the North Pacific Ocean, sets out to land to find the boy she saved from a shipwreck seven years before, the boy she entrusted her pink pearl. She eventually found the boy, named Kaito Domoto. But the human form Lucia assumed, a girl named Lucia Nanami, doesn't have any resemblance to her mermaid form. But she also cannot tell Kaito who she really is; otherwise she would turn into foam. So she tries to convince Kaito into figuring out who she really is.

At the same time, Lucia has been told that a group of sea monsters or suiyo have invaded the marine world and she had to gather the six other Mermaid Princesses and their pearls to resurrect the legendary goddess Aqua Regina to stop them. So to fulfill this, she joins forces with Hanon and Rina, both Mermaid Princesses who also came up to dry land, use their pearls, turn into singing idols, and use their voices as an offensive.