Following the catastrophic Armageddon, the world has been overrun by vampires, posing a new threat to humanity. The ongoing conflicts between Methuselah (vampires) and Terrans (humans) have divided the planet into distinct factions. Methuselah have established the New Human Empire, while Terrans occupy the Vatican Papal State. Despite the factions' efforts to avoid direct conflict, the strained relations between them have been exacerbated by the Rosenkreuz Order, which is intent on instigating a new war. To combat extremist groups, the Vatican has established the AX unit, which targets organizations engaged in terrorism. Under the leadership of Cardinal Caterina Sforza, AX agents investigate confrontations involving vampires and strive to bring about peaceful coexistence between Methuselah and Terrans. Priest Abel Nightroad, a seemingly disoriented individual with extraordinary vampire slaying skills, is a member of the AX unit. Accompanying him is Sister Esther Blanchett, a brave and compassionate nun with a difficult past. As Abel and Esther grow closer, they begin to uncover a sinister force that is manipulating events behind the scenes. However, their journey is fraught with adversity, forcing them to confront their own emotional trauma.