Mermaid (aka Mei ren yu) is 2016 Chinese movie about mermaids.
Thousands of years ago some of the humans ancestors were forced into the sea, they adapted, and evolved into mermaids.
In 2016, a rich businessman, Liu Xuan, bought the Green Gulf on the auction for 20.08 billion. After learning that the dolphins have left the area, he managed to get a reclamation order for the bay. He then used sonar transmitters to monitor the bay, and use them to prevent dolphins from returning.
Shan is a mermaid who had her tail cut, so she could disguise herself as human and go on land. She has trained hard to stand on the end on her tail, and imitate walking. The mermaids plan to use Shan to seduce Liu Xuan, and then lure him into a trap, so they could kill him for what he did to the waters. Shan managed to sneak into one of Liu Xuan parties and give him her number.
After having a a small fight with his girlfriend, Li Ruolan, Liu Xuan called Shan as a joke, but his security men though he meant it, and picked her up. The mermaids were ready to kill him, but Liu Xuan himself wasn't with the security men. After an incident with the security check, Shan snuck into Liu Xuan office and tried to kill him, but constantly missed him, due to unforeseen acts. Eventually Liu Xuan unknowingly knocked Shan out. And when she came to, he offered her money so she would leave. Liu Xuan even drove her into city, planning to ditch her, but eventually grow curious of her. Shan had lead her into her workplace, where she cooks chicken, and they had a good time, singing and going on a roller-coasters.
In the evening Liu Xuan drove Shan home, and she invited him for tea. At the last moment she asked what he would do if he had one minute to live, and he answered that he would only look her, because he loves her. Shan then closed the door in his face to save his life.
The next day Liu Xuan asked Shan out again. The octopus also sneaked to the meeting as a chef. He was about to kill Liu Xuan, but then his security men arrived and he changed his mind. The octopus even sacrificed two of his tentacles to keep the masquerade up. After the octopus couldn't take it anymore, and jumped out of the window, Liu Xuan ordered his men to leave and proposed to Shan. Shan fought Liu Xuan on the decision, and even revealed him that she is lying to him, and she was supposed to kill him. Shan stormed out when Liu Xuan's lover and business partner showed up. Later that night, Liu Xuan went to Shan's to surprise her, but what he saw was the surprise, Shan was a mermaid, and in her room was the octopus, and other mermaids. Liu Xuan was captured and taken to the shipwreck, where the mermaids were hiding.
There the mermaids were about to kill Liu Xuan, but Shan saved him, and told him to run. Liu Xuan managed to get a away, and went to the police, to make a report of his kidnapping, but they wouldn't believe him. Liu Xuan started to research the mermaids, and other marine life. He never thought about his effect on the environment before. Liu Xuan then tested the sonar on himself, and after learning that they only used 1/10 of it's power, he wanted the shareholders to shut down the sonars. Li Ruolan arrived and supported Liu Xuan's decision. Feeling he could trust her, Liu Xuan revealed the existence and location of the mermaids.
Li Ruolan had a revelation of her own, she had funded Liu Xuan's scientist to find living mermaids after they had found two dead ones. Liu Xuan protested and urged them to stop, but Li Ruolan only wanted to make more money and had no care for morals. Li Ruolan went with a private military force to capture the mermaids, and to kill every single one who tried to escape. Hundreds of mermaids were killed, before the elder mermaid used her powers to bend water. Realizing that Liu Xuan didn't lie about trying to help them and that the sonars were off, several mermaids managed to escape the shipwreck and dive deep into the ocean. Shan was caught trying to escape, with a harpoon, and a fierce chase took place, nearly killing Shan. Li Ruolan used a rocket launcher to blast Shan out of the water. Liu Xuan had managed to get out of the traffic jam he was stuck with Cheng's jetpack, and saved Shan from being shot dead. He then carried Shan to the end of the pier, but Li Ruolan shot several harpoons in their direction hitting Liu Xuan three times.
Liu Xuan survived through that, and donated all his money to protect the environment. He married Shan who took a new name, Lucy, to hide her identity.