Mermaid princess Ha Ni falls for Shi Kyung and becomes human, moving into In Gyeo House, a residence for job seekers. To stay human permanently, she must make Shi Kyung love her in 100 days.

Ha-Ni (Jo Bo-Ah) is a mermaid. For a man she is in love with, she becomes a human being and begins to live at the Ingyeo House. The house is for people who are preparing to land their first jobs. To permanently become a human being, Ha-Ni must make the man love her within 100 days.—AsianWiki