Sito, a young mermaid boy with green scales, lives in a colorful underwater world. One day, he meets Lila, a mermaid with red hair and a blue tail, who sings wonderfully. They become friends and explore the coral gardens together, play hide and seek with the fish, and discover an old treasure chest. Lila shares with Sito a human mirror she found, and they dream of worlds above the waves. Every day, they meet to share adventures and laughter, becoming best friends under the sea.