lucia, the mermaid princess from the north pacific, lands in search of the boy she saved from the sea seven years ago when the boy drowned, she saved his life with pink beads and handed over her most precious pink pearl to the man bbb。 seven years later, she came to the land to find the former boy to return to maju, and finally found the boy named domoto hito, but lucia, who transformed into a human form, was not similar to her mermaid form; she could not tell hito her true identity, otherwise she would become a bubble. therefore, she tried hard to let haidou think of her true identity. meanwhile, lucia knew that a group of water monsters had invaded the sea world. she must gather seven mermaid princesses and their beads to revive the legendary goddess of the ocean, akan rezina, and to stop the conspiracy of the water demons. in this way, she joined forces with six other mermaid princesses boeing, lena, cherryn, noel, coco and saro who came to the land to use their pearls to become singing idols and use their singing as attack weapons to deal with the water demon.