Five-year-old Sosuke grew up in a seaside town on the edge of a cliff. One day Sosuke found a waste glass bottle washed ashore by the waves. There is a trapped little goldfish named Boni Mermaid. The queen's daughter sneaked out to play with jellyfish and bumped into a bottle. Sosuke took Boni back to her plastic basin. Sosuke Sosuke's family had a good time and enjoyed it. However, the happy days passed quickly. Boni's father Fujiwara took his daughter back to the bottom of the sea. A fisherman later fell in love with the mermaid queen and became a seafloor dweller? Boni missed Sosuke very much after returning home and made a bold decision-to become a person with Sosuke. With the help of her sisters, Boni stole her father's magic weapon and swam to the human world. Unexpectedly, the water of life contains dangerous magic. The sea was out of control, and the two sisters became terrible giant fish. The waves rushed to the cliff of the broker ... Boni didn't expect that his good wishes would bring such a disaster. Can he save Sosuke?