In 1575, Katsuyori invaded Mikawa Province, leading 15,000 soldiers (8,000 to 10,000 soldiers, according to one theory) to subdue Sadayoshi OKUDAIRA and his son Nobumasa, who had switched sides to Ieyasu TOKUGAWA in the previous year.
天正3年（1575年）、勝頼は先年徳川家康に寝返った奥平親子を討伐するために兵1万5000（一説には8000から1万）を率いて三河国へ侵入した。