The story is about a student named Kei Nagai, who discovers he is an immortal "Ajin" when he is hit by a truck. He becomes a wanted person because the Ajin are considered dangerous inhuman beings and the only person who is there to support him is his childhood friend, Kaito. While the government claims to help Ajin live in a safe environment, they are actually using them as subjects for cruel and inhumane experimentation. As a result, Ajin that have escaped are bent on revenge with the exception of Kei. During his escape it is subtly revealed he lacks the capacity for empathy and throughout the series only shows an interest in his own goals, pointing to the conclusion that Kei has antisocial personality disorder.