During the day, Saya Kisaragi portrays the role of a peaceful schoolgirl, while at night, she transforms into a fierce monster hunter, utilizing her father's ceremonial sword to guard her village from any potential danger. Nonetheless, when she becomes aware of a broken covenant announced by the monsters, her convictions and the reality itself are brought into question. A mysterious dog approaches her about her pledge to protect the village, causing Saya to experience unexplainable visions. As her world begins to fall apart, she sets out on a voyage to reveal the authenticity in a village where things may not always be what they seem.