After his return to Japan, Ōsumi served as Director of the Bureau of Naval Affairs in 1922, and was promoted to vice admiral in 1924, Vice Minister of the Navy in 1925, commander-in-chief of the IJN 2nd Fleet in 1928, and Commander in Chief of the Yokosuka Naval District in 1929. He was promoted to full admiral on 1 April 1930. Ōsumi was a strong proponent of Japan's southward expansion, but refused to align himself with either the Treaty Faction or the Fleet Faction within the Navy. He was awarded the Order of the Sacred Treasures, 1st class on 14 May 1931.