In the Taisho-era Tokyo of 1923, vampire numbers climb as an artificial blood source called Ascra spreads through the city. The army answers with Code Zero, a covert unit staffed almost entirely by vampires under the human major Yoshinobu Maeda. His first assignment is Misaki Nakajima, a stage actress killed by a falling prop and revived as a vampire, who now answers mostly in lines from Salome. Maeda has to judge whether she can be trained for the unit while the military weighs how far it will go to turn the undead into weapons.