He subsequently served as an instructor at the Army Academy and in a number of staff roles, including a diplomatic mission to Germany in May 1902.

He was promoted to colonel in March 1905 and major general in January 1909 and was given command of the IJA 19th Infantry Brigade.

[1] In August 1919, Ōi became the commanding officer of the Vladivostok Expeditionary Force[2] and in November of this same year was promoted to full general.

[citation needed] Ōi was ennobled with the kazoku peerage title of danshaku (baron) in April 1921,[4] and entered the reserves in March 1923.

Despite this, he was still purged by the American occupation forces after World War II, and returned to his native Yamaguchi Prefecture.