Anazawa Toshimitsu served as a bushō and retainer of the Ashina clan, and as the lord of Iwayama Castle in Mutsu Province during the Sengoku and Azuchi-Momoyama periods.
While serving the Ashina clan, Toshimitsu governed Hinohara in the Yama District of Mutsu Province from Iwayama Castle. Hinohara was on the northern edge of the Ashina domain, located between the Azuma ridge lines running east to west. The base of operations for the Date clan was situated in Yonezawa to the north. As a result, Toshimitsu was continually exposed to the threat of attack by the Date.
In 1565, Toshimitsu and his father, Anazawa Toshitsune, repelled an attack on Toyama Castle by Ishikawa Tajima-no-kami, a retainer of Date Terumune. In 1566, Toshimitsu repulsed a surprise attack by the Date forces at Iwayama Castle. However, late in 1584, a member of the family named Anazawa Shirō兵衛 (who had been in conflict with Toshimitsu) colluded with Date Masamune. Through the connections of Shirō兵衛, Masamune dispatched 1,500 soldiers for a lightening attack on Hinohara. The Date forces also blocked roads in the direction of Ōshio. With no path of retreat, the Anazawa forces fell into confusion and many died in battle. Toshimitsu fought valiantly from Iwayama Castle, but after it fell, he killed himself along with other family members.
Thereafter, Masamune built Hinohara Castle on Mount Odani to the south of Iwayama Castle. He assigned Gōtō Nobuyasu as guardian. There is also a theory that Masamune himself attacked and toppled Iwayama Castle in the spring of 1585. Anazawa Toshitsugu, the eldest son of Toshimitsu, was not present at the time of the attack so he escaped a disaster, and later entered Kashiwagi Castle. After the extinction of the Ashina clan, Toshimitsu served Gamō Ujisato and his descendants served as retainers of the Aizu-Matsudaira family.