 When Hideyoshi engaged in a campaign in the Chūgoku region, Mitsunari assisted his lord in attacks against castles like the Tottori Castle and Takamatsu Castle (in present-day Okayama).After Hideyoshi seized power, Mitsunari became known as a talented financial manager due to his knowledge and skill at calculation.From 1585 onward, he was the administrator of Sakai, a role he took together with his elder brother Ishida Masazumi.