Mizuki Henmi is an adolescent girl who is acquainted with Shu Suzuri, a quiet young man who runs an old Japanese bookstore. She is the granddaughter of the building's landlord. During a routine visit to the shop, Mizuki learns about a mysterious and valuable book that Shu plans to sell. Her unrestrained and somewhat impulsive nature leads her to handle the book roughly, accidentally breaking the seal that had kept it shut and releasing a small, seemingly cute spider. As the story progresses, Mizuki becomes increasingly cautious and wary of the creature and its actions, standing in contrast to Shu, who grows infatuated with the spider. Her skeptical and alert demeanor serves as the voice of concern within the group, driving much of the tension in the narrative. Mizuki's primary motivation appears to be protecting herself and those around her from the potential danger that the spider represents. Her key relationship is with Shu Suzuri, as their differing reactions to the spider create the central dynamic of the story. Her development is marked by a shift from curiosity to wariness as she realizes the creature may not be as harmless as it first appears. Mizuki possesses no supernatural abilities; her notable trait is her perceptiveness and caution, which often put her at odds with Shu's more trusting outlook.