Shogun's Gold in America

It is the Kyoho Era, during the reign of Tokugawa Yoshimune, and the shogunate is in the midst of an economic crisis. However, they have a trump card which could be the key to breaking them out of these dire straits--the "Tokugawa Buried Gold", a massive sum of gold left behind by the first Tokugawa shogun, Ieyasu! With a map to its location, the ninja Kojiro heads off to find it. That location? America--the New World--still divided between the indigenous peoples and the colonists! There Kojiro meets a Native girl who has a mysterious connection to the buried gold...