Surplus Princess is a story about a mermaid who attempts to become a human being so that she can stay forever with the man she loves.
Ha Ni (Jo Bo Ah)is a mermaid princess in the underwater empire but she loves for the human world when she sees and falls in love with a man. She transforms into a human and follows Hyun Myung (Ohn Joo Wan)to live in a temporary house for people who are preparing for employment. The pragmatic Hyun Myung is trying to find a good-paying jobto provide him with a comfortable life. But will he be distracted by HaNi, who has just 100 days to make Hyun Myung fall in love with her so that she can permanently remain as a human being?