日向国
Hideyasu took part in his first campaign during the Kyūshū Campaign of 1587, leading the assault on Buzen-Iwaishi Castle. He also received honors for his distinction in the pacification of Hyūga Province. Hideyasu also took part in the Siege of Odawara (1590) and the Japanese invasions of Korea (1592–98). His successes in these campaigns earned him respect as an able field commander, despite his youth.