In August, 1180, Hirotsune raised an army to defeat the Heike and wiped out the Heike's party in Kazusa Province when MINAMOTO no Yoritomo had attempted to re-raise an army in Awa Province after losing the Battle of Ishibashiyama and joined forces with Yoritomo's force and his 20,000 horse soldiers.
治承4年（1180年）8月に打倒平氏の兵を挙げ、9月の石橋山の戦いに敗れた源頼朝が、安房国で再挙を図ると、広常は上総国内の平家方を掃討し、2万騎の大軍を率いて頼朝のもとへ参陣した。