Saya begins her morning meditating on a light that continues to escape her grasp. Her trance is broken by her father reminding her to hurry up if she wants to eat breakfast before school. At school she converses with her friends before having to head home early to their disappointment.

At home her father hands her a katana and tells her to slay the Elder Bairn.

Saya keeps spending her days happily at school while hiding her duties as a hunter of Furukimono from her classmates. Itsuki Tomofusa, the class president, does his best to have Saya respond to his feelings without success, while she shows concern for Shinichirō Tokizane, another classmate who rarely speaks to her, but usually watches her from afar.

Saya learns that the bakery owner is missing and soon finds that a Furukimono is behind his disappearance. She fails to save his life, but manages to slay the creature, who speaks to Saya about a "Conevant" before passing away.

Shinichirō gets Saya to tell her about the Furukimonos, offering to be her confidant. As Saya returns home, she finds Tadoyoshi collapsed on the floor, though he passes it off as a dizzy spell. As the dog talks to Saya, asking her what would happen if she broke the promise she made, she experiences another headache as she recalls something concerning a reward and a punishment. After a few days of no Furukimono activity, Saya returns to school, where a Furukimono appears and attacks the class, killing several students. With no escape available, Saya is forced unsheath her katana in front of her friends to fight the Furkimono.

Kanako, Nene and Nono, along with Shinichirō who also appears, reveal themselves to be part of a 'main cast', playing roles for the purpose of making Saya remember who she is in order to be rewarded with their own desires. As they force Saya to drink Furukimono blood, which she had allegedly been drinking whenever she became passed out, they reveal she is linked to Shrovetide, a period in time where demons are given permission to eat humans. As Saya starts to remember things as a result of drinking the blood, a Furukimono appears and the group are confronted by Itsuki, Yūka and Fumito, who question their motives for disobeying the project.

Saya finally remembers that, having been captured by Fumito, she had her memories altered and was put on a stage to feed on Furukimonos as a test to see if she would change. Fumito has the Furukimono to kill Shinichiro, Nene and Nono for disobeying their orders. Saya kills the Furukimono before it can kill Kanako, but she is instead killed by Takayoshi who is revealed to be half-Furukimono that has gone beserk from drinking Saya's blood. As Saya fights against Tadayoshi, she manages to obtain a powerful light, allowing her to defeat him. As Fumito makes his escape, sending an army of multiplying Furukimono to kill everyone in town, Itsuki sacrifices himself in order to protect Saya, admitting he had fallen for her before passing away. After beating the Furukimono, Saya tries to attack Fumito before he escapes, but is shot in the head. Left along on the island, Saya treats herself and prepares to make her next move.