Secret of the Twin Swords

In 1730, the Tokugawa Shogunate orders the Yagyu Clan to repair a huge shrine. Since it cannot refuse the Shogunate's request, the impoverished Yagyu Clan tries to raise funds by obtaining a sword which holds the key to a wondrous, hidden treasure. After learning the sword's secret, Tange Sazen sides with the Yagyu Clan, but his motive seems to be more than just pure interest in the treasure...