Mukoujima Takurou's intense fascination for fishing blossoms during his high school years, but takes an unexpected turn when he reels in an adorable, pig-tailed mermaid named Muromi-san who speaks with a distinctive Hakata dialect. In no time, Muromi-san becomes a frequent visitor to Takurou and brings along her mermaid friends: Sumida-san, Fuji-san, Levia-san, and Hii-chan. What's more interesting is that Takurou's fishing spot attracts not only mythical creatures like the Yeti and Harpy but also makes his fishing expeditions even more thrilling.