The deep-sea mermaid tribe believes that removing the bone spurs from their fish tails allows them to go ashore and become human. Mermaid Xiyin, born with zero spurs, was sent to land, only to discover that the so-called ascension is a conglomerate's conspiracy. Escaping back to the deep sea by luck, she is not believed by her tribe and allies with Mochuan, who is investigating in secret. The two gather evidence and expose the leader Heisha's scam of colluding with humans at the grand ceremony. The conglomerate is captured by the maritime security, and the mermaid tribe breaks through the illusory fantasy to guard their deep-sea homeland.