Kei Nagai

Driven by a profound desire to cure his sister, Eriko, this brilliant and studious young man strives to become a medical pioneer. As an Ajin, he initially presents a cold, highly analytical personality, prioritizing logic over emotional connections. However, beneath his detached exterior lies a person of deep principle who values the bond with Kaito. While he acknowledges the brutal methods used to secure his freedom, he remains steadfast in his opposition to unnecessary violence.