Born in 1118 as head of the powerful Chiba clan of Shimosa Province. In August 1180, when Minamoto no Yoritomo fled to Awa after the defeat at Ishibashiyama, the 63-year-old Tsunetane rallied his entire clan and threw full support behind Yoritomo's revival. The Chiba forces—said to number 20,000—dramatically swelled Yoritomo's army and laid the groundwork for controlling Kanto. Tsunetane reportedly advised Yoritomo to base himself at Kamakura, making him a key architect of the shogunate. He subsequently joined the campaigns against the Taira in western Japan and, despite his advanced years, participated in the Oshu expedition against the Fujiwara in 1189. Appointed guardian of Shimosa, the Chiba clan secured its place as one of Kanto's greatest vassal houses. Tsunetane died in 1201 at the venerable age of 84. The Chiba clan's crescent-and-stars crest is said to be the origin of Chiba Prefecture's emblem.

Despite his advanced age, a decisive and loyal warrior who supported Yoritomo's comeback. Possessed both leadership over his clan and strategic foresight.

An indispensable contributor to Yoritomo's success. The Chiba clan thrived as major Kanto vassals, and their crescent-moon crest is said to have inspired Chiba Prefecture's emblem.