Kei Nagai is an ordinary high school student until he dies in a traffic accident and suddenly comes back to life. He discovers that he is an Ajin, an immortal being feared and hunted by the government. Forced to run away from society, Kei becomes involved in a violent conflict between humans and other Ajin. As he struggles to survive, he uncovers the dark truth behind how Ajin are treated and used. The story combines intense action, psychological tension, and battles between immortal beings.