Lifespan: 14xx to 9/18 of Bunmei 3 (1471)
Rank: shugo daimyō
Title: Assistant Vice Minister of the Sovereign’s Household
Bakufu: Muromachi – Military Governor of Hōki Province
Father: Yamana Noriyuki
Siblings: Toyoyuki, Toyouji, Motoyuki, Kōtarō, others
Wife: Daughter of Ōdachi Motofusa
Children: Masayuki, Hisayuki, daughter (wife of Ōdachi Hisauji) (there were another son with an unknown name and several other daughters)
Yamana Toyoyuki served as a shugo daimyō during the Muromachi period. Toyoyuki was the military governor of Hōki Province.
Toyoyuki was born as the eldest son of Yamana Noriyuki. At the time of his coming-of-age ceremony, he received one of the characters in his name from Yamana Mochitoyo (Sōzen), a shugo daimyō and the head of the main branch of the Yamana family.
While not certain, Toyoyuki may have inherited the headship of the clan around the seventh month of 1453. Toyoyuki, however, was placed under the direction of his father, and, rather than act as a military governor, he spent a majority of his lifetime in the capital of Kyōto serving as an attendant to Ashikaga Yoshimasa, the eighth shōgun of the Muromachi bakufu. Nevertheless, Toyoyuki gradually acquired the authority of the military governor and, in the eighth month of 1461, the bakufu allowed him to render an opinion in regard to the recognition of the Tajima 聚慶軒 territory held by his younger brother, Yamana Toyouji (the military governor of Inaba) in the Miwa township in Inaba Province.
Despite their role as military governors, the Ōnin-Bunmei War weakened the authority of the Yamana over their territory in Hōki and elsewhere, whereas collateral families and kokujin, or provincial landowners, showed signs of exercising their autonomy, further fostering instability. In the first month of 1467, Toyoyuki was summoned to Kyōto along with his father, Yamana Sōzen (the head of the main branch of the Yamana family) and his son, Masayuki. Around 1469, he traveled from Kyōto to Hōki Province in a failed bid to help bring under control the chaos in the region arising from the Ōnin-Bunmei War. In the ninth month of 1471, Toyoyuki was murdered in Shima in the Yura township of Hōki. The act was committed by retainers who rebelled against the Yamana family. According to one theory, this event was related to a confrontation between the Yamana of Hōki and the Amago clan along with powerful kokujin. This event involving the Yamana served as a trigger plunging the residents of Hōki and the surrounding area into an era of upheaval.
Toyoyuki’s murder occurred prior to the death of his father, Noriyuki, in 1473, so Toyoyuki did not formally inherit the role of military governor.