Saion is a minor adult male character who works as a librarian. He appears barefoot. When the protagonist Rin visits the library to research folklore and disturbing phenomena, he interacts with her. Saion possesses knowledge of "spirit bugs," entities from ancient mythology believed to be otherworldly beings capable of influencing unconscious minds. He warns Rin that her ability to see these spirit bugs may be an ominous portent, potentially foretelling her death. His role provides exposition, connecting the narrative's mythological elements, government conspiracy, and psychological horror. Through his dialogue, Saion helps link the threads of serial killings, wartime experiments, and Rin's personal journey.