Saya Kisaragi appears to be a typical, clumsy high school student living in a quiet, rural town with her father, Tadayoshi. By day, she attends classes and enjoys her favorite café, but by night, she fulfills a sacred duty inherited from her late mother: hunting "Elder Bairns," grotesque, otherworldly monsters that feed on human flesh. Saya wields a ceremonial sword, fighting these creatures to protect the townsfolk, often experiencing strange gaps in her memory and recurring visions that hint at a deeper, buried truth about her existence.As the series progresses, the attacks become increasingly brutal, claiming the lives of her friends and classmates in horrific, visceral displays of carnage. Saya grows emotionally distraught, struggling to balance her peaceful facade with the trauma of these violent encounters. However, the town itself is revealed to be a carefully constructed stage. The inhabitants are not ordinary citizens, but actors participating in a twisted
social experiment orchestrated by the enigmatic Fumito Nanahara.Fumito, a man Saya trusts implicitly, has been manipulating her life to test the limits of her combat abilities and physiological endurance. The "Elder Bairns" were unleashed to force Saya into a state of constant, desperate battle, while her memories were suppressed through chemical intervention to keep her docile and unaware of her true nature. The climax shatters the illusion entirely: the town is destroyed, and the survivors are slaughtered as
the experiment concludes. Saya discovers that she is actually an artificial being—a human-vampire hybrid engineered to consume the blood of her own kind.Betrayed by everyone she held dear, Saya’s personality shifts from gentle and naive to cold and vengeful. She realizes that her memories of a "normal" life were merely manufactured scenarios designed to harvest data on her lethality. With the experiment complete and her purpose unmasked, Saya finally breaks free from her psychological conditioning. Fueled by righteous fury and the realization of her true identity, she vows to hunt down Fumito. The story concludes with Saya surviving the wreckage of her former life, now fully awakened, prepared to exact violent retribution against those who turned her existence into a gruesome, blood-soaked spectacle for their own amusement.