The anime is based off an old Japanese story, which in turn was inspired by the classic Chinese novel Suikoden (Water Margin).

In the original story, a large band of outlaws are given amnesty by the government to fight foreign forces and rebels. The Tenpou Suidoken version relocates the story to the Chiba Prefecture town of Tonosho, and it revolves around the chivalrous battles of Sasagawa no Shigezou and Iioka Sukegorou.

(Source: Anime News Network)