Kei Nagai

Kei Nagai is an Ajin and the main protagonist of the series. Kei was first shown with an academic serious personality. He is very intelligent and hardworking with ambitions to be a doctor who cures illnesses that dont yet have a cure specifically to cure his sister Eriko. Despite Keis lack of emotional investment in others he seems to have strong personal values that he tries to live by. He demonstrates gratitude for Kaitos help and cares about his welfare. He also doesnt begrudge Sat for having killed others to free him but does not support killing more people unnecessarily. Source: Ajin Wiki