Namiko is a naive mermaid with a pink tail, flowing silver hair, and the most beautiful voice. It is her dream to sing of love and hope to her beloved Eiji, a member of ExciTe, a Japanese pop-duo who happens to be searching for a special maiden. Following the melody beset by her dreams of romance, Namiko flies from the Atlantic region to Japan. Despite chasing this personal love-story, Namiko carries with her the divine commission given to all Merpeople by The Father of Love with her.
The human world declines more and more as it slips further and further into the influence of the Shadows, causing humans to forget love and seek decadent independence which is the source of the world's chaos. Merpeople are commissioned to sing to all humans, teaching them of true love and a coming new world of peace. However, the queen of Shadows, Lady Sin and her warriors seek to eradicate all Merpeople along with their songs to preserve the current world and advance human progression. By gathering "Progeny", humans who embrace shadows, Lady Sin seeks to awaken the "Heir to the Light Bearer" who will revive an ancient kingdom, sealing the fate of the world's future.
Upon arriving in Japan, after an unexpected chance to meet her beloved Eiji being squandered, Namiko meets a mysterious traveling music conductor and a dapper owl named Oliver. During their exchange, she is gifted a special pearl of divine power and is revealed to be Pearl Maiden, the one who will seal away the Shadows.
Namiko takes on her mission with a wistful reluctance as the mysterious songs of ExciTe tug at her very soul. Not knowing that Eiji and his partner Teppei hold deep secrets of their own, Namiko is teased with constant chances of the long-awaited rendezvous as the peridot-eyed celebrity reaches out to her. However, the enemy continues to advance, rapidly coming ever closer to awakening the Heir who will transform the world into an empire of shadows.
With the future of the world at stake, Namiko must ask herself a question to which the answer seals the fate of the world: "What's more important: Her love? Or her Duty?"
