Lifespan: Entoku 3 (1491) to 1/6 of Tenbun 11 (1542)
Name Changes: Katsumasa → Sukemasa
Other Names: Shinsaburō, Bizen-no-kami, Kyūgai-Sōgo (monk’s name)
Father: Azai Naotane
Adoptive Father: Azai Naomasa
Mother: Sister of Akao Norimasa
Wife: [Formal] Azai Kuraya (daughter of Azai Naomasa), [Consort] Amago Kyōan
Children: Hisamasa, Takamasa, Masahiro, Hidemasa, Yamashiro-no-kami, Kaizu-dono (Azai Tsuruchiyo), 松市-Goryō (wife of Mitamura Sadayori), daughter (wife of Azai Tadatane), Chiyozuru (wife of Rokkaku Muneyoshi), Ōmi-no-kata (wife of Saitō Yoshitatsu)
Adopted Children: Taya Akimasa
Azai Sukemasa served as the lord of the Azai clan of northern Ōmi Province.
Sukemasa was born in 1491 as the son of Azai Naotane, a kokujin from northern Ōmi and branch family of the main Azai clan. He wed the daughter of his cousin, Azai Naomasa, who was of direct lineage to the main clan, enabling Sukemasa to become a lineal heir. Sukemasa’s rise to power is an example of gekokujō, a phenomenon made possible during the tumult of the Sengoku period by which retainers usurped the power of their former rulers.
At the time that Sukemasa became lord of the clan, the Azai served as hikan, meaning kokujin who supported the Kyōgoku clan, shugo of the northern portion of Ōmi. After Kyōgoku Takakiyo, the head of the Kyōgoku, expressed his intention for his second son, Kyōgoku Takayoshi, to be his designated heir, a struggle for succession broke out within the clan. Sukemasa, together with Asami Sadanori, a kunishū from Ōmi, promoted Takakiyo’s eldest son, Kyōgoku Takanobu, to become the successor, creating a confrontation with Takakiyo. Sukemasa and Sadanori were expelled by their lord, Takakiyo, Takayoshi, and Uesaka Nobumitsu to Owari Province. Thereafter, Sukemasa played a central role in leading riots by kokujin against the Kyōgoku in Ōmi. Sadanori acted tyrannical, so Sukemasa banished him, became the leader of the kokujin resistance, and seized power away from the Kyōgoku.
Having established a base of power in northern Ōmi, the expansion of Sukemasa’s domain led to conflict with Rokkaku Sadayori, the military governor of southern Ōmi. The Rokkaku were lineal descendants of the Genji-Sasaki clan of Ōmi, commensurate with the main Kyōgoku clan. During this period, the Rokkaku were on the rise, protecting the Ashikaga family and participating in the Muromachi bakufu. In the beginning, Sukemasa was at a disadvantage relative to the Rokkaku and subject to frequent incursions. However, after acquiring control over the kokujin class in northern Ōmi, he was able to narrowly overcome these attacks.
Meanwhile, Sukemasa’s excesses in the conduct of his governance bred dissatisfaction among the Kyōgoku who had become figureheads. This prompted Takanobu to reconcile with his father, Takakiyo, who joined with Nobumitsu and a following of kokujin to oppose Sukemasa. Owing to his standing conflict with the Rokkaku, Sukemasa did not have the resources needed to confront the Kyōgoku so, in 1534, he settled with Takanobu and Takakiyo.
In 1541, Takanobu rebelled against Sukemasa a second time. Sukemasa died early in 1542 prior to resolution of the conflict with the Kyōgoku. Following his death, his eldest son, Azai Hisamasa, fought with Taya Akimasa, his son-in-law adopted into the family, for control of the clan. Akimasa joined with Takanobu to attack Hisamasa, so Hisamasa submitted to the Rokkaku for protection.