The year is 1614 AD. Two warring ninja clans, each supporting a son of Hidetada Tokugawa as the next shogun, send ten representatives each to fight to the death for the possession Tokugawa government for the winning clan for the next thousand years.
- At the dawn of Japan's Azuchi-Momoyama period (the late 16th century) two rival ninja clans, the Iga Tsubagakure and Kouga Manjidani, are engaged in a bitter blood feud that has spanned for centuries. The fighting finally ends when Hattori Hanzo the 1st succeeds in forging a cease fire between the two clans by conscripting both into the service of Tokugawa Ieyasu (the man who seized power to become Shogun and form Japan's first truly stable form of centralized government). Regardless, hostilities and bad blood remain between Kouga and Iga, ensuring a tenuous co-existence at best.
Fast forward to the year 1614; Ieyasu has retired from power (although he still wields considerable influence within the government) and passed the torch to his son Hidetada. Unfortunately, a succession dispute has risen concerning which of Ieyasu's grandsons are destined to take up the reins of power when their father finally decides to step down. The various government retainers are beginning to take sides and the Tokugawa Shogunate is on the verge of tearing itself apart.
In order to solve the problem before it spirals out of control, Ieyasu orders the no hostilities pact between Kouga and Iga canceled and promptly commands each clan to send 10 of their best ninja to enter a ruthless and bloody competition of kill or be killed. The leaders of the two clans kill each other off outside of the walls of the palace, leaving nine ninjas in each side to determine the outcome of the battle.