Lifespan: 15xx to Eiroku 7 (1564) (estimated)
Rank: sengoku daimyō
Bakufu: Muromachi – military governor of Inaba
Father: Yamana Toyosada
Mother: Daughter of Hosokawa Takakuni
Siblings: Toyokazu, Toyokuni
Children: 豊儀 (?)
Yamana Toyokazu served as a sengoku daimyō in Inaba Province during the Sengoku period.
Toyokazu was born as the eldest son of Yamana Toyosada of the Tajima-Yamana clan. His mother was the daughter of Hosokawa Takakuni.
Toyosada died in 1560. Toyokazu’s cousin, Yamana Munetoyo, succeeded Toyosada as the lord of Inaba Province. Munetoyo was the eldest son of Yamana Suketoyo (Toyosada’s older brother). In the fifth month of 1561, however, Munetoyo died at the age of eighteen. As a result, Toyokazu assumed the role of lord of Inaba. Toyokazu first appears in historical records in a letter of commendation dated 6/20 of Eiroku 5 (1562). As noted, he appeared to have inherited the headship of the clan following the death of Munetoyo.
At this time in Inaba, kokujin, or provincial landowners, primarily in the Yakami and Hattō districts sought independence from the governance of the Tajima-Inaba clan, so the Yamana were not able to pacify them. Toyokazu was anxious about the prospect of battling against these local families.
In the midst of this instability, in 1563, a senior retainer named Takeda Takanobu launched a rebellion against Toyokazu, backing Yamana Toyohiro to serve as the new military governor. In the fourth month, Toyokazu attacked the base of Takanobu at Tottori Castle, but lost a senior retainer from the Nakamura clan en route to a defeat at the Battle of Yutokoroguchi. in the winter of that same year, a counterattack by the Takeda forces ousted Toyokazu from his base for the military governor at Fuse-Tenjinyama Castle, forcing him to flee to Shikano Castle.
Toyokazu and his forces received support from Yamana Sōsen (the name adopted by Suketoyo after entering the priesthood), but the Takeda forces benefited from support from the Mōri clan and kokujin from Hōki Province under the command of the Mōri. As a result, Toyokazu’s forces continued to be at a disadvantage. In the seventh month of 1564, these forces approached the foothills of Shikano Castle.
Thereafter, Toyokazu no longer appears in historical records. In the third month of 1565, Yamana 豊儀 appears as a likely successor, so that, Toyokazu is surmised to have either died in the siege of Shikano Castle or retired. There are also theories that Yamana 豊儀 was another name for Toyokazu’s younger brother, Yamana Toyokuni or that it was the real name of the son of Yamana Hisamichi named Genshichirō.