Before the Osaka Summer Campaign, Tokugawa Ieyasu gathered his retainers, including Yagyu Tajima and Hattori Hanzo, at Edo Castle for a meeting. At the meeting, Tajima discovers a ninja of the Sarutobi-ryu style lurking behind the ceiling and immediately orders Hattori Hanzo, the leader of the official secret society, to pursue him. Hanzo wants to eliminate the Sarutobi-ninja under the command of Yukimura Sanada, an enemy of Ieyasu, and meets a boy named Sasuke on his way to pursue them.

At the same time, Tajima, who had determined that the covert group led by Hanzo could not eliminate the Sarutobi Ninja alone, was in pursuit of the Sarutobi Ninja using the Yagyu Shinobi under his control. Eventually, one of the Yagyu ninja killed the Sarutobi ninja, but he was killed by the newly emerged Sarutobi ninja. Hattori Hanzo, who witnessed the whole event, learned that the Sarutobi Ninja were not actually alone, but that all those who used Sarutobi's techniques called themselves Sarutobi Ninja (ninja monkey group).