text: On August 21, The Eastern army alliance which sided with Ieyasu Tokugawa attacked Takegahana castle which defended by Oda Hidenobu, who sides with Mitsunari faction. They split themselves into two groups, where 18,000 soldiers led by Ikeda Terumasa  and Asano Yoshinaga went to the river crossing, while 16,000 soldiers led by Naomasa, Fukushima Masanori, Hosokawa Tadaoki, Kyogoku Kochi, Kuroda Nagamasa, Katō Yoshiaki, Tōdō Takatora, Tanaka Yoshimasa, and Honda Tadakatsu went downstream at Ichinomiya. The first group led by Terumasa crossed the Kiso River and engaged in a battle at Yoneno, causing the Hidenobu army routed. On the other hand, Takegahana castle were reinforced by a Western army faction's general named Sugiura Shigekatsu. The Eastern army led by Naomasa and Fukushima crossed the river and directly attacked Takegahana Castle at 9:00 AM on the August 22nd. Shigekatsu himself setting the castle on fire and committed suicide as a final act of defiance.
  On September 29, Tadakatsu and Masanori led their army to rendezvous with Ikeda Terumasa army, where they engaged Oda Hidenobu army in the Battle of Gifu Castle. crossing a river near Hagiwara and Ogoe town, and approached the Gifu Castle with total 35,000 soldiers. In this battle, Hidenobu castle were deprived  the expected support from Ishikawa Sadakiyo (石川貞清), who decided to not help the Western army in this war after he made an agreement with Naomasa. Hidenobu was prepared to commit seppuku, but was persuaded by Ikeda Terumasa and others to surrender to the eastern forces, and the Gifu Castle fell.
  In October, Tadakatsu participated in the Battle of Kuisegawa. At first, two Tokugawa generals Nakamura Kazuhide and Arima Toyouji fell into a trap of ambush from the flanks as they were pursuing the fleeing Western Army officers Shima Sakon and Akashi Teruzumi. However, the timely intervention of Tadakatsu gave space for Kazuhide and Toyouji to escape from Sakon aggression, and Tadakatsu managed to halt the western army from pursuing his comrades.