In 1599, Yoshitsugu gathered his men and moved with the Tokugawa troops as far as
Tarui Castle. According to the Keicho Kenmonshu, Mitsunari was at Sawayama Castle and invited Yoshitsugu to his realm. Though blind due to his illness as he entered the gates, Yoshitsugu was appalled to find armed soldiers awaiting him and developed a silent grudge toward Mitsunari. Undeterred, Mitsunari introduced him to his vassal,
Shima Kiyooki. Kiyooki flipped Yoshitsugu's perceptions of the Western army, but he wanted to remain within Ieyasu's ranks as he believed Mitsunari could not win. However, for one reason or another, Mitsunari was able to convince Yoshitsugu to defect and join the Western army. His other activities before the Battle of Sekigahara are not clearly known, but he was said to have suggested Mitsunari to relocate his main base the night before the conflict. Yoshitsugu led an army of 6,500 for the battle, he was command 600 troops and had three subordinates:
Hitatsuka Tamehiro with 900 troops, his son,
Ōtani Yoshikatsu, with approximately 2,500, and
Kinoshita Yoritsugu with 1,000. Other daimyo under command of Yoshitsugu:
Toda Katsushige with 1,500 troops. During the battle, Yoshitsugu's troops was outnumbered in a successful attack led by Kobayakawa Hideaki; Yoshitsugu committed suicide and his troops retreated shortly thereafter. Amidst the confusion within the Otani clan troops,
Toda Katsushige was slain by the Tokugawa forces.}} The Ōtani retreat left the Western Army's right flank wide open, which Masanori and Hideaki then exploited to roll the flank of the Western Army. Mitsunari, realizing the situation was desperate, also began retreating his troops. Meanwhile, Western Army commander
Shima Sakon was engaged by the troops of
Kuroda Nagamasa, who had taken a detour on the north to flank the Mitsunari and Sakon positions. In the end, Sakon was shot and fatally wounded by a round from an arquebus. ==In popular culture==