Olivia was born into a world with a special virus. This virus converts people from normal humans into monster hybrids, like werewolves, vampires, dragons, and many more.
The world has accepted it, for the most part. Olivia lives in the "good" part of the world, where people can live together peacefully whether they're human or monster.
But there are less utopian places. Out in the Outskirts are huge towns of tents and people trying to get into the cities. They are hunted by the Orix, dangerous shadow monsters that prey on humans and monsters alike.
Olivia is one of the few people still human at her age. But when she has a car accident and goes to the hospital, she finally becomes her monster form.
Then she and her friends, and the rest of the university she goes to, take an Aptitude Test, meant to classify them in the defense forces.