After a battlefield attack turns him into a vampire, the soldier Shutaro Kurusu is folded into Code Zero, a secret Imperial Army unit hunting supernatural threats in 1920s Tokyo. His childhood friend Aoi Shirase, now a newspaper reporter, keeps crossing paths with vampires in the course of her assignments, unaware that one of them, watching from a distance, is the man she believes died in the war. The manga retells the story of Mars Red, which began as a staged reading.