The Kouga and Iga ninja clans each harbour a bitter animosity towards the other but are restrained from battle by a 400 year-old covenant of peace. However, Gennosuke of Kouga and Oboro of Iga have a love for one another, and being the heirs of each clan, will soon unite the two sides with their marriage.

Just when it looks like the two sides may be reconciled a scroll surfaces, listing the names of twenty ninjas, ten each from the two clans. It announces that the covenant has been broken, and that they must eliminate the members of the opposing side. What they don't know is that each side will represent an heir to the Tokugawa Shogunate, and the victorious side will determine the next leader of the empire.

The ban on warfare has been lifted and the battle is quickly enjoined. Blood feuds and centuries-old grudges are remembered and the ninjas use their unique techniques and strange bodies to wreak havoc on their enemies.

Can the love of two ninjas survive in this sea of hatred? Or are they destined to lead their clans to a bloody end?