Content Warning: This section references sexual assault, sexual coercion, and abuse.

In the world in which Reia Salvias lives, demons are a constant threat to humankind. Demons enjoy the scent of human fear and lurk near houses, villages, towns, and other human settlements to devour people. They emit clicking and howling sounds that alert people to their presence. Towns draw the greatest number of demons due to the intense scent of fear, so they have guards and walls of wooden spikes to keep the demons out. Demons vary in size: The larger the demon, the more people they have eaten. They also vary in appearance, usually with black skin, human-shaped heads, and bodies comprised of different animal parts. Some have horns, some have feathers, some have fur, and some have wings.

To avoid demons, humans either live in clearings to prevent demons from hiding in the trees or seek refuge within the walls of a town. Demons can only come out at night. During the day, they retreat to their home in the Veil. Duskwalkers live alongside demons in the Veil but can walk in sunlight. They speak like humans but, like demons, enjoy the scent of fear and eat people.