24-year-old Kai seems like the perfect main character of a romance drama: handsome, a graduate of a prestigious university, and the son of the famous jewelry brand Tears of Mermaid. But this seemingly perfect man has a secret. He is a Merman. While Mermen are born human, they transform into Mermen when they fall in love and are tragically fated to leave for the sea, forced to leave their loved ones behind on land. It's the pesky hormone -- oxytocin, a.k.a. the love hormone -- which triggers the Merman transformation, making it impossible for Mermen to breathe on land. Determined to survive on land, Kai keeps his distance away from women until the formidable Yana comes crashing into his life. Kai faces the ultimate test for survival in this fantasy, romance, adventure drama as he discovers the meaning of true love, sacrificing and risking everything for Yana, the first love of his dreams.