Kaede Murakami lives with her family on an island in the Seto Inland Sea. The family's livelihood is threatened when a ferry ship route to the island may be closed for good. Her family are also the descendents of Takeyoshi Murakami. Takeyoshi Murakami was the general of samurai pirates known as “Murakami Suigun”. Their group loved freedom and the sea, while they battled Hideyoshi Toyotomi. Meanwhile, a legend has it that the samurai pirates stashed treasures away nearby. Kaede decides to set out with three classmates to unravel the secret of the samurai pirate treasures.