Donten ni Warau

In 1878, Japan is still scarred by the fall of the samurai order and the ban on carrying swords. Former warriors angry at the new government fuel violent unrest, and authorities respond by building a massive prison in the middle of Lake Biwa. The Kumou brothers, Tenka, Soramaru, and Chuutarou, help capture criminals and ferry them across the lake.

The brothers' lively home hides a growing threat. An ancient calamity known as Orochi is said to return every 300 years by taking a human vessel, and signs of its rebirth begin appearing around Oumi. As government agents, ninja clans, and other factions search for that vessel, the Kumou family's peaceful routine is pulled into a struggle over who will seal Orochi and who intends to use its power.