Kei Nagai, a high-school student, should have died when the truck hit him. Instead, he comes back to life and his world is changed forever. Kei learns he is an Ajin or demi-human, a mysterious creature that cannot die. Frightened by the prospect of what might happen to him, Kei, helped by his friend, Kai, flee from civilization only to encounter a group of demi-humans who are hostile to humans. Who should Kei side with?