Curious, but do you know what part of Japan he may be from? My mother's maiden name is Sato. She is from Kyushu. I believe most of her family is either from Nagasaki or Sasebo area (both her mom and dad side).
My Great Grandmother was Chizu Nogami, married Shuichi Nagashima. They had two children: Kenichi and Emiko. Kenichi took his father's surname when Chizu passed away. I can't remember my Grandfather's first name, but it starts with an "M". Sato is his last name.