长州藩
Born in Kokura (in present-day Kitakyūshū) to a "samurai" family of the Kokura Domain in Buzen Province, Oku joined the military forces of the nearby Chōshū Domain during the First and Second Chōshū expeditions and the Boshin War in their struggle to overthrow the Tokugawa shogunate and bring about the Meiji Restoration.