Legend speaks of the fourth primogenitor, the most powerful vampire confined to the realm of myths. But when this being masters the 12 sacred beasts, a vampiric catastrophe looms over Japan. To thwart this threat, the government's Lion organization dispatches a skilled magician known as a 'sword shaman' to eliminate the fourth primogenitor. However, the chosen spy turns out to be a novice sword shaman named Himeragi Yukina, unaware of her true mission.