The warlord, Oda Nobunaga, is rapidly vanquishing his foes on a quest to pacify and unify the country under his rule. However, there is one region that even Nobunaga fears: The Iga Province, home to the Iga ninja, known to be extraordinary weapons of war who do not think of people as human and will assassinate anyone for money. There is one Iga ninja, Mumon, who is renowned as a deadly assassin and who has unmatched battle strength, earning him the nickname of Iga's strongest ninja. However, he is equally lazy and only seeks to earn money to please his wife, Okuni. At the same time, a ninja named Heibee Shimoyama becomes disillusioned with his people's way of living.