From pg. 4 of user manual:
Three years have passed since the young swordsman, Yoshitsune Minamoto, and his warrior-monk companion, Benkei Musashibo, defeated the Heishi Clan and their leader in a brutal battle over the possession of "Amahagane" -- divine jewels that bring their owners godlike powers like Kamui. With success, it had finally seemed that peace, however temporary, had arrived.
During this time, Yoritomo Minamoto, Yohshitsune's older brother and leader of the Genji Clan, tracked the remnants of the Heishi to the south of Japan where he and his army were preparing to eliminate their weakened numbers. However, rumors begun to spread of new, ungodly creatures appearing within the Heishi ranks and their evil force re-strengthening, even without the use of the Amahagane.
Now, with the aid of his closest friends and some unlikely allies, Yoshitsune must once again wield his fierce blades and summon the powers of the Amahagane in an epic battle to save all of Japan.