The chapter opens with a flashback to a time when humans were fighting against half-demons. The narrator explains that half of the demons were allowed to remain at the school, but that the other half were put on a blacklist and killed if they were caught. He explains that black foxes, a type of fox that lives on human life force, are addicted to it. They do not live on it, but crave it. Because they are self-sustaining, they do not have to hunt for food. They have learned to live on their own, so they are not subject to the blacklist, but remain a "key subject" to be kept on.