Satou's origin story is what anyone would expect from a special forces soldier - a loose cannon who doesn't excel at social niceties. His fascination with Ajin, after his unit is involved in one of the first captures, makes him a psychopath in waiting. But it's when he's stationed in Africa that the real chaos with Fox ensues, changing the course of human history. Satou is right - the problem with Ajin is that you never know until you die. They look and act like us, making it a seductive idea for someone like Fox, a super-soldier who is bored with his job. Fox is willingto take the ultimate test and effectively becomes an Ajin after he's dishonorably discharged for going rogue during a mission. For someone like Satou, being an Ajin is the greatest gift available - an unending supply of extra lives. It's exactly where the Satou we knew as a great villain would have come from, making this origin story as authentic as it gets.