Ko Nakano is a young Ajin who appears in the anime series. He is of average height and build, with short light brown hair and reddish‑brown eyes. His most distinctive facial feature is his thick, dark eyebrows, and he is usually seen in casual clothing such as a t‑shirt or hoodie and jeans.

Ko is impulsive, somewhat clumsy, and not quick to grasp complex situations. He often fails to understand figurative language or subtle cues and tends to act on instinct rather than formulating careful plans. Despite these limitations, he possesses a strong sense of right and wrong and is not afraid to break away from those he considers dangerous.

Initially, Ko was taken in by the older and more ruthless Ajin known as Satou. When Satou revealed his violent and destructive intentions, Ko balked and escaped, seeking out Kei Nagai to ask for help. Although Kei was initially distrustful and even trapped him temporarily, Ko eventually convinced Kei to work together to stop Satou. This partnership marks his central role in the story: as a secondary Ajin ally who provides a more earnest and less calculating perspective compared to the other immortal characters.

Ko’s most notable limitation as an Ajin is his inability to summon an Invisible Black Matter (IBM), the ghost‑like familiar that most Ajin can control. This forces him to rely on physical strength, weapons, and his own regenerative immortality in combat. Over the course of the series, he becomes more confident and committed to confronting Satou, though he never develops the strategic thinking of his companions.

His key relationships are with Kei Nagai, whom he initially distrusts but later respects as a partner; with Satou, his former mentor turned adversary; and briefly with other members of the anti‑Satou group. His character arc centers on rejecting manipulation, finding his own purpose, and contributing to the fight against a common threat despite his shortcomings.