The Blue Whisper

Chinese fantasy show The Blue Whisper features all sorts of celestial, immortal and fantastical beings, and merfolk are one of them. The main character is Ji Yunhe, a spiritual master who is trying to gain enough resources to pursue an independent life, and her love interest is Chang Yi (Ren Jialun), a merman prince who has been captured. The powerful Fairy Shunde wants Chang Yi to be broken into becoming her loyal servant, and Yunhe is one of two spiritual masters who take the task of training him.

It's one of those shows where almost everyone is playing 4D chess and has layers of intentions and deceptions and occasional truths. Yunhe uses gentleness to manipulate Chang Yi into growing attached to her, and along the way she falls in love with him in return despite herself. That's the plot to start with, but further enemies and allies and agendas upend the situation.

Chang Yi is a main character and his identity as a merman is critical to everything that happens to him, from his powers, limited knowledge of land and emotionally merfolk fall in love only once in their lives. But the story is entirely on land and there's so many other characters and creatures that this is kind of swallowed up. We only see his (CGI) tail in the first two episodes of season one, briefly in episode 9 when he gives up his tail, and even more briefly in the show finale after he has regained his tail. Chang Yi's father the Sea King appears and Chang Yi later has loyal merman attendant Luo Suo (Li Bao Er) to help him, but all these mermen have legs.