The intro may depict a duel between the Uesugi and Takeda (after all, in Shogun II, the Uesugi are depicted, rather ahistorically, as the monk faction even though the ikko ikki were often aligned with the Takeda against the Uesugi) and this event may have a basis in history. In 1564, both armies met once again at Kawanakajima and matters were settled with a duel rather than a battle as in the case of the rather memorable previous meeting in 1561. Unlike the intro in Shogun II, the duel between the Uesugi champion and the Takeda champion resulted in the Uesugi triumphing and the Takeda restoring some lands in Shinano province to Murakami Yoshikiyo, a Uesugi ally and a daimyo dispossessed of his lands by Takeda Shingen's invasion of the province.

Source: Murdoch, James and Isoh Yamagata. A History of Japan During the Century of Early Foreign Intercourse (1542-1651)