At Yachimata, there is a legend of a deity named Tayutayu-sama who protected the area, but this deity and other so-called "Tayutai" have been lost in time. Mito and his friends discover a relic on the school grounds with mysterious patterns on it. Then, at the opening ceremony of the new school year, an equally mysterious girl named Mashiro appears before Mito. Mashiro is somehow tied to the relic and the legend of Tayutayu-sama.

Nagasumi's in hot water after a beautiful, young mermaid named Sun saves him from drowning. The deep-sea sweetheart's dad is a merman yakuza prone to executing anyone who learns his family's scaly secret! Luckily, there's a catch - if Nagasumi agrees to marry Sun, he just might avoid sleeping with the fishes!