Ieyasu convinced some that the in fighting was between the members of the toyotomi clan. Some who had a dislike for mitsunari used this as a way to both get rid of him while showing loyalty to the toyotomi (Kato Kiyomasa, Fukushima).

Kobayakawa was stationed away from Mitsunari on the field, and he had already been meeting with the Tokugawa beforehand along with the Mōri, Kikkawa. When the main fighting began, mitsunari, Konishi, and Ukita engaged the eastern army forces multiple times.Reinforcements from mt.nangu and matsuo would have won the battle, but once the Mōri betrayed, the dominoes fell (kobayakawa and kikkawa betrayed), and Ishida got routed, hunted down, and executed.