Hiroie was Kikkawa Motoharu's son and succeeded his elder brother Motonaga when the latter died in 1587. He ruled the former Amako domain and was one of the most powerful men in the Môri clan, later leading troops under his cousin Môri Terumoto in the 1st and 2nd Korean Campaigns. When sides were being drawn between Ishida Mitsunari and Tokugawa Ieyasu, Hiroie urged Terumoto to side with the latter, a recommendation that Terumoto did not specifically decline (despite going along with Ishida), thus prompting Hiroie to send a secret message to Ieyasu to the effect that he could count on the Môri to do nothing in the coming fight. In the Battle of Sekigahara, Hiroie, with 3,000 men, occupied the lead position in the Môri army deployed on the east side of Mt. Nangû - when the fighting began he refused to move, thus preventing Môri Hidemoto (with 15,000 men) from entering the fray. After the battle, Hiroie was disappointed to discover that Ieyasu had no intention of rewarding the Môri for their inactivity, though he did increase Hiroie's own fief somewhat. Hiroie built Iwakuni castle in 1608.
- Initial text from Samurai-Archives.com FWSeal & CEWest, 2005