In a world where the sudden appearance of an immortal being, known as an Ajin, sparks fear and ruthless government pursuit, high school student Kei Nagai discovers he is one of them after a near-fatal accident. Terrified and confused, Kei is thrust into a desperate fight for survival as he is hunted by a relentless task force determined to capture and experiment on him. His only ally is his loyal friend, Kai, who risks everything to help him escape. However, Kei's flight for freedom becomes even more perilous when he crosses paths with a radical and charismatic rogue Ajin who seeks to use their kind's powers to wage a violent war against humanity. This dark, thrilling anime explores themes of identity, morality, and the monstrous nature of fear, as Kei is forced to confront not only the world that despises him but also the terrifying, shadowy entity that resides within his own soul.