Takuro is a high-school boy who loves fishing. One day he landed a lovely mermaid, named Muromi-san who speaks Hakata dialect. She looks about the same age as Takuro, but is actually a very old legendary creature, and her sisters and she are guardians of the Earth. Muromi-san and her gang brings Takuro to an extraordinary adventures. High-tenshon slapstick comedy based on the best-selling comic.