A Jin, a koi from Bibo Pool, suffered a heavenly tribulation three hundred years ago and was saved by the scholar Xiao Chengyan. Taking human form to go ashore and fulfill the debt-of-gratitude vow of the "three returns and three tribulations," she sheds her scales through her trials. The two join hands to fight against the powerful minister Pei Xiang and the black koi Liu Ruyan, rescue A Jin's mother, and uncover the sealed secrets of the dragon vein and ancestral dragon. After experiencing life-and-death bonds, binding their lives together, and defeating the black jade crisis, they hold a wedding ceremony at the Gratitude Pavilion, only to encounter a new storm, exhausting the love, hatred, and protection between demons and humans.