At Yokota Base in Japan, American soldiers stand guard at the brink of the Vietnam War. Although they fear the enemy outside their base, an even more dangerous enemy waits within - bloodthirsty vampires walk among them. Appearing human, the beasts lurk in secret among the soldiers, waiting for the moment to attack. Saya, a fierce and beautiful vampire hunter, is sent to lead a team of undercover agents whose mission is to decide who is human and who is not, and wipe out the vampires before they can wipe out the base. But even though Saya is a powerful warrior whose skill with her Japanese sword is lethal, her ferocity may not be enough.