Kei Nagai and Kou Nakano, having narrowly escaped death, hatch a plan to avenge themselves against Satou - a fellow Ajin seeking to rule the world. Satou's series of public killings prompts humanity to search for a solution to defeat the immortal enemy. Kei unexpectedly teams up with former adversaries Yuu Tosaki, a high-ranking government official who possesses tactical knowledge on Ajin, and Tosaki's Ajin assistant, Izumi Shimomura. Together, they gather allies to halt Satou's crusade, racing against time to prevent the ruin of civilization.