The Great Duel 1964

A cynical samurai is left as the sole survivor to fulfill a plot to assassinate the puppet of a villain intent on usurping the shogunate in the 17th century. A Shogunate Elder connives to rule Japan by making his puppet, the Shogun's brother Tsunashige, the next Shogun. The best strategist in Japan, Yamaga, leads a plot to stop the Elder, but his cabal is betrayed and most of the conspirators are captured and tortured.