San is a mermaid and Seonghwa is a human. Even though they are from two different worlds they became childhood friends. San had fallen in love with Seonghwa, and Seonghwa had fallen for San as well. One day everything changed for the two friends when Seonghwa moved to a different town after his father passed, leaving San all alone. Years later Seonghwa was a pirate, and a member of an infamous pirate crew, and he was in a relationship with the captain, Hongjoong. What will happen when a familiar mermaid joins the crew and enters Seonghwa's life once again?