A sadistic Daimyo (feudal lord) rapes a woman and murders both her and her husband, but even when one of his own vassals commits suicide to bring attention to the crime, the matter is quickly hushed up. Not only will there be no punishment, but because the Daimyo is the Shogun's younger brother, he will soon be appointed to a high political position from which he could wreak even more havoc. Convinced that the fate of the Shogunate hangs in the balance, a plot is hatched to assassinate the Daimyo. The two most brilliant strategic minds of their generation find themselves pitted against each other; one is tasked to defend a man he despises, and has a small army at his disposal. The other is given a suicide mission, and has 12 brave men. They are the 13 Assassins.
When Kanbe Nagakichi has his turf taken over by Ano-Toku, the father-in-law of his sworn brother Kira Nikichi sets in motion one of the most violent gang battles in Japanese history. Forced by the situation to choose between family and yakuza honor, Nikichi faces off against the vile combination of Ano-Toku and Kurokoma Katsuzo, villains so low as to ambush their foes using snipers. Nikichi, who owes allegiance to Boss Jirocho of Shimizu asks Jirocho to spare Ano-Toku’s life until events force a showdown between the 30 member Shimizu gang and a force of over 200 men fighting on Ano-Toku’s behalf. Meanwhile, a mysterious samurai may hold the key to deciding the outcome of this battle!