He is TERRA'S Strategic Operations Vice Commander and his rank is Major. He takes over the Command in Kunugi's absence. He is always smiling, but he is a dependable man at heart. He is Kim's secret boyfriend, and the two seem very happy together from the few scenes they share.
Lieutenant of TERRA at 22 years old. Second in command at TERRA and has a big role near the end of the series in framing Makoto and getting him fired. After Elvy finds out Ayato is a Mulian the two have a loud argument, and Ayato overhears, which is the first time he actually realises he is a Mulian. Souichi is clearly fond of Ayato and believes that regardless of whether or not Ayato is a Mulian, he is still himself and thus, should be looked at as an individual. Yagumo gives him a heart to heart telling him that its who he is that matters and not the colour of his blood.
During the Tuning he is killed by Ayato. After the Tuning he is alive as seen with him appearing on the TV set, hopefully sharing his life with Kim.