Kamata Harumichi served as a bushō during the Sengoku and Azuchi-Momoyama periods. He was a retainer of Waga Tadachika.
Harumichi served the Waga clan who governed the Waga District of Mutsu Province. Harumichi was an active participant in the Waga-Hienuki Uprising led by Waga Yoshitada in 1590 and the Iwasaki Uprising led by Waga Tadachika (Yoshitada’s son) in 1600. Originally, however, Harumichi was not a retainer of the Waga clan. He was dispatched by the Date clan to serve as a guard for Waga Tadachika. He is considered to have been an expert swordsman.
In 1590, during the Oushū Retribution (the Oushū shioki) by Toyotomi Hideyoshi, after the Hienuki clan was ruined, Hideyoshi assigned Asano Nagamasa as his representative to Toyagasaki Castle. After Nagamasa returned to Kyōto, Asano Shigeyoshi remained in the castle. In the winter of the same year, the Waga and Hienuki clans launched the Waga-Hienuki Uprising in an effort to recover their former territories. During this uprising, Harumichi appears in records among the bushō who rushed to the territory of Waga Yoshitada to regain control of Toyagasaki Castle. By this means, the Waga and Hienuki recovered the castle and the former territory of the Hienuki clan but, in 1591, the Toyotomi forces invaded again and suppressed the uprising. Meanwhile, Yoshitada was captured and killed by locals.
In the wake of these events, Waga Tadachika turned to Date Masamune and resided in the Isawa District in the Date territory. In 1600, at the time of the Battle of Sekigahara, Masamune sought to expand his territory so he gave secret orders to Tadachika, whereupon Tadachika launched the Iwasaki Uprising in a bid to recover the Waga District. Harumichi supported Tadachika in this effort.
Based at Futago Castle, the Waga forces invaded the Waga District governed by Nanbu Yoshinao and stormed Hanamaki Castle (earlier known as Toyagasaki Castle) in addition to other outlying castles in an event known as the Nighttime Attack on Hanamaki Castle. The forces breached the third and second citadels and pressured the main citadel but valiant fighting by the Nanbu forces repelled them. Meanwhile, the Nanbu recaptured Futago Castle so the Waga forces moved to hole-up in Iwasaki Castle. In the middle of the tenth month, the main contingent of the Nanbu forces led by Nanbu Toshinao and Kita Nobuchika arrived, while a battalion led by Suzuki Yoshinobu came in support of the Waga forces, leading to fierce clashes. In the end, however, Iwasaki Castle fell, and, aware of imminent defeat, Tadachika and his retainers fled to Sendai territory. During their escape, at Ishinazaka, the Waga forces threw stones from higher ground at the Nanbu forces pursuing them. The Nanbu forces fought back by throwing stones from below, but the Waga forces distanced themselves from the Nanbu who feared the stones thrown from above, enabling the Waga to safely reach the Sendai territory. Thereafter, the forces fled to the Kokubunni Temple in Sendai but, Tadachika, together with close retainers including Harumichi, Tsutsui Kinosuke, and Saitō Jūzō, took their own lives at the temple.
In 1720, the great-grandchild of Tadachika named Waga Naoyoshi built a memorial for him at the Kokubunni Temple.