Seungri is Merman boy with white hair and white tail. He has a tattoo on the right hand as sign he was a Merman and this mark also status because Seungri is son of  King in the kingdom of the sea. Seungri didn't like other merman or mermaid, he was very curious about human and life on the land after he read mermaid princess legend so he always comes to the surface to see human and human life there.

One time Seungri saw a boy on a cruise ship, but whatever the cause tat boy fell into the sea from cruise ship. Seungri help the boy and took him to a cave. And they become friends and often meet but that boy had to go back to Seoul, then Seungri give his blue crystal necklace as his liaison with that boy.

A few years later Seungri met the wizard who can turn him became human. Seungri required to drink the poison to be human and risking his life. Because the wizard only gives three months on Seungri to be human. If within three months he couldn't prove true love between the two of them his heart will became black and pread to his body and then Seungri will be bubble and disappear. 

Can Seungri prove his true love with that boy? Or the legend will repeat again?