"Ajin" is a dark fantasy anime series based on the manga by Gamon Sakurai. The story centers on Kei Nagai, a high school student who discovers he is an Ajin, a rare type of immortal human, after surviving a fatal accident. Ajin are feared and hunted by society due to their perceived threat and inhumane nature, often subjected to brutal experimentation by governments and private organizations. Kei is forced to flee and live as a fugitive, grappling with his new identity and the moral dilemmas it presents.

As Kei evades capture, he encounters other Ajin, including Sato, a charismatic yet ruthless figure who leads a militant group of Ajin seeking to overthrow the oppressive systems that target them. Sato's methods are extreme, involving violent attacks on government facilities and public institutions, which further fuels societal fear and hatred of Ajin. Kei is torn between his desire for survival and his reluctance to embrace the violent path Sato advocates.

The narrative explores themes of identity, morality, and the consequences of immortality. Kei's journey is marked by his struggle to retain his humanity while navigating a world that views him as a monster. The series delves into the psychological and ethical challenges faced by Ajin, particularly their ability to regenerate from injuries and summon an invisible, powerful entity known as an IBM (Invisible Black Matter). These abilities make Ajin both formidable and vulnerable, as they are hunted for their unique traits.

Supporting characters include Kaito, Kei's loyal friend who aids him despite the risks, and Izumi Shimomura, a government agent and fellow Ajin who initially opposes Kei but later becomes an ally. The dynamic between these characters adds depth to the story, highlighting the complexities of trust and betrayal in a world where survival is paramount.

The plot is driven by intense action sequences, strategic confrontations, and moral quandaries, as Kei and other Ajin navigate a society that seeks to exploit or eliminate them. The series maintains a tense, suspenseful atmosphere, with a focus on the psychological toll of immortality and the ethical implications of using power for survival or vengeance. "Ajin" presents a gripping narrative that challenges conventional notions of humanity and morality within a dystopian framework.