It's 1923, and Tokyo is in danger! A surge in vampires caused by the illegal trade of an artificial blood source, "Ascra," has provoked a vampire crisis. In response, Lieutenant General Sounosuke Nakajima has ordered the formation of a special military unit, Code Zero. This group is made up of vampires and tasked with finding the source of the Ascra trade and capturing and killing vampires.
Colonel Yoshinobu Maeda is in charge of Code Zero and he is under a lot of pressure to get results, or the unit will be disbanded. Even more difficult is the fact that the vampires in the unit are trying to understand and control their new powers and identities. It's up to them to quell the crisis or be consumed by their demonic natures.