Set in 1844, the sadistic Lord Naritsugu is rising to power and murders and rapes at will, no one can touch him because his brother is the current Shogun, a government official decides something must be done before he rises too far and a trusted samurai is hired to ambush the Lord on his way home from Edo, 12 samurai are initially gathered with the 13th member (with supposed samurai lineage but I believe really a forest or mountain demon) found in the forests on their trek to a town which has been bought as the point to ambush the Lord and his 70 followers. The problem is he now has 200 followers and the last part of the movie is set for the ambush.
The director of this movie is Takashi Miike (I have only ever seen his Ichi the Killer as a movie and as a manga and it still makes me flinch to this day) but he has toned down his violence and bloodshed a little for this. The movie is a brooding visual marathon for most of the movie, the Lord is a sadist and you will feel too that he needs to go (some of the stuff is quite awful), there is some action in the first three quarters of the movie but it all a set up for the epic action at the end between the 13 and 200 and this is what it could have been called, some of the 13 are stone cold killing machines, while others are barely able to hold their own but sometimes numbers count for nothing in confined areas as the village has been booby trapped and specifically designed to split up the forces of Lord Naritsugu, there is bow, sword, spear, gunpowder and flaming bullocks (strange, very strange) action here.
This is an epic ending and the reason for the 4 STARS (you could basically skip to it every time), my favourite character is Kiga who they enlist (well free him from a basket suspended from a tree) when they meet in the forest (and is responsible for the best dialogue, rock throwing and geisha/brothel house destruction and not in the way you might think).
Will have to find the original now and I believe the movie is set on real events which led to the Meiji restoration in the 1860's.