In 1923, a vampire crisis befalls Tokyo. Provoked by the illegal trade of "Ascra," an artificial blood source, the population of vampires grows rapidly within the city. Under orders from Lieutenant General Nakajima, the Special Forces Unit 16 gathers vampires within the military to create a new undercover vampire-hunting unit called Code Zero. With the world at odds against them, the members of Code Zero must find a way to curb the crisis or otherwise fall victim to their own demonic natures