What was the biggest battle in medieval Japan's history?

The biggest battle in medieval Japan's history is often considered the Battle of Sekigahara, fought on October 21, 1600. This pivotal conflict determined the future of Japan and marked the beginning of the Tokugawa shogunate, which ruled for over 250 years. The battle involved a clash between the forces loyal to Tokugawa Ieyasu and those supporting the Western Army led by Ishida Mitsunari, ultimately resulting in Tokugawa's decisive victory and the unification of Japan under his leadership.