He also had a large part in the refurbishing and expansion of the base. Two years later, MSF began operations from Mother Base, an offshore plant from which Kaz gave radio support. Kaz's persistent refusal led him to decide to hold a contest first to determine if he'd join, which ended in Big Boss's favor and Kaz finally joining MSF. There, he met Big Boss, who tried to convince him to join Militaires Sans Frontières. In 1972, Kaz got a position as a drill sergeant for a band of revolutionaries in Colombia.
After his mother died, he began to drift around the world as a mercenary and philanderer. The JSDF life wasn't what he had hoped for, and he went back to America, only to find out his father was dead and buried. Shortly after his return to Japan, Kaz joined the Japanese Self-Defense Forces both to pay for his mother's hospital bills and to see what the battlefield is like. When Kaz went to America, he discovered he had a half-brother who had recently died in the Vietnam War. Sometime, he came across a photo of his father whom he never met an American soldier eventually came into the store and recognized him as Colonel Miller.
Kaz's early life was difficult, as he was unable to obtain Japanese citizenship among a lot of other factors including his mother becoming ill and having to run her shop by himself when he was only ten years old. His mother named him after the Japanese word for "peace" (和平). He was born in Yokosuka of the Kanagawa Prefecture, Japan. Kazuhira Miller was the son of an American GHQ officer and a Japanese prostitute.