Ajin: Demi-Human follows Kei Nagai, a high school student who discovers he is an Ajin, an immortal being who cannot die and can summon a powerful ghost-like entity called an IBM. After a fatal accident reveals his nature, he becomes the target of a government that views Ajin as dangerous test subjects. The story shifts between his desperate escape from capture and the actions of other Ajin, including the ruthless and charismatic terrorist Satō, who uses his immortality to wage a violent war against humanity. Readers enjoy the series for its tense, cat-and-mouse plot, the strategic and tactical action sequences, and the morally complex characters who each have different philosophies on what it means to be immortal in a world that fears them. The dark, realistic art style and the psychological horror of being hunted also add to the gripping, mature tone.