The most powerful lord of Kazusa Province, said to command 20,000 horsemen—the largest force in Kanto. In 1180, he joined Yoritomo's uprising but arrived late and was severely scolded. Swallowing his pride, he continued to serve and contributed enormously to the campaigns that established the shogunate. However, his independent spirit and habit of treating Yoritomo as an equal rather than a lord became an intolerable threat to Yoritomo's drive for centralized power. In January 1184, Kajiwara Kagetoki, acting on Yoritomo's orders, suddenly cut Hirotsune down in the middle of a board game. The killing was framed as a preemptive strike against rebellion. Yet after his death, a prayer was found inside his armor—a fervent wish for Yoritomo's military success and the Minamoto's victory. When Yoritomo learned of this, he reportedly felt deep remorse, as recorded in the Azuma Kagami. This tragedy has endured as one of the starkest illustrations of Yoritomo's ruthless exercise of power.

Bold and proud, confident in commanding Kanto's largest army. He treated Yoritomo as an equal rather than a lord, yet was secretly deeply loyal.

Known as a tragic vassal purged by Yoritomo. The story of the prayer found after his death, contrasting Yoritomo's ruthlessness with Hirotsune's loyalty, has been widely depicted in literature.