An Xin'er comes from a rich family, but suffers from ichthyosis and is tortured by this disease. She was deceived by her scumbag boyfriend, who put her in danger, and she accidentally falls into the sea. Fortunately, she is rescued by Yu Sheng, an alien from the planet Kepler, and a legendary merman. As the king of the sea, Yu Sheng is simple, kind and naive.