In post-World War II Japan, Saya, a mysterious and stoic young girl, is a skilled swordswoman with a dark secret: she is a vampire. Under the guise of a student, she is tasked by a covert government agency to hunt down and exterminate demonic creatures known as Chiropterans, who disguise themselves as humans and prey on the unsuspecting. As part of her mission, Saya is sent to a U.S. Air Force base in the 1960s, where she enrolls in a high school on the premises. There, she comes into contact with several characters, including the school nurse, who become inadvertently entangled in her deadly quest.

As Saya delves deeper, the line between predator and protector blurs. Tension and violence escalate as Chiropterans reveal themselves amidst the student body, leading to brutal confrontations. The base becomes a battleground where Saya's lethal efficiency and resolve are tested to their limits. With each encounter, scenes of intense action and harrowing suspense unfold, showcasing Saya’s relentless pursuit and the terrifying reality of the demonic threat. The narrative teases out the complexities of Saya's identity, her burden, and the high stakes of her mission without revealing the ultimate resolution.