Lifespan: Entoku 1 (1489) (?) to Eiroku 7 (1564)
Other Names: Suruga-no-kami, Suruga-no-kami Sadamitsu, 宇駿, 宇駿 Sadamitsu, Shirōemon-no-jō (common)
Clan: Usami (descended from the Kudō branch of the Fujiwara-Nanke)
Lord: Jōjō Sadanori → Nagao Harukage → Nagao Kagetora (Uesugi Kenshin)
Father: Usami Fusatada
Children: Sadakatsu (?), Katsuyuki (?)
Usami Sadamitsu served as a bushō during the Sengoku period. He exercised power from Biwajima Castle in Echigo Province. According to military stories, Sadamitsu served as a military strategist for Uesugi Kenshin, but this cannot be confirmed from authenticated accounts. He serves as the model for a fictitious character named Usami Sadayuki who appears in war stories as a military strategist of Kenshin.
Period prior to succession by Nagao Kagetora
Sadamitsu’s activities are confirmed in primary sources where he is variously referred to as Usami Suruga-no-kami, Usami Suruga-no-kami Sadamitsu, 宇駿, and 宇駿 Sadamitsu. He allied with Uesugi Sadazane, the military governor of Echigo and, in 1514, defeated and killed a foe of Nagao Tamekage (the deputy military governor) named Usami Yashichirō Fusatada at Echigo-Iwate Castle. In historical accounts, the individual noted as the son of Yashichirō who fled the castle at this time is deemed to be Sadamitsu while Fusatada was his father. Meanwhile, an individual named Usami Takatada is regarded as the same person as Fusatada under an earlier name.
Approximately twenty years after the fall of Iwate Castle, Sadamitsu appears in records as a bushō on the side of Jōjō Sadanori (a member of the Uesugi family serving as military governors of Echigo) in opposition to Nagao Tamekage during the Echigo Kyōroku-Tenbun Conflict. Initially, Sadamitsu aligned with Tamekage but later abandoned him, formulated a range of schemes, and, in the fifth month of 1535, amassed along with members of the Ueda, the Tsumari, the Yabugami, and the Ōkuma in support of Sadanori. On 4/10 of Tenbun 5 (1536), at the Battle of Sanbun-Ichihara, the combined forces of the Usami and Kakizaki were defeated by Tamekage’s men, but, after the battle, Tamekage retired so the outcome still proved fruitful for Sadamitsu. According to one theory, during this battle, the Usami forces led by Sadamitsu were cornered just before killing Tamekage. Moreover, an individual named Usami Shirōemon-no-jō served as a bushō on behalf of Sadanori. This may have been a reference to Sadamitsu but, according to some sources, was another individual.
Period after succession by Nagao Kagetora
In 1548, after Nagao Kagetora (Uesugi Kenshin) inherited the headship of the clan, Sadamitsu obeyed him and entered a stronghold to prepare for an attack by Nagao Masakage, the head of the Ueda-Nagao family opposed to Kagetora. According to a letter addressed to Tairako Magotarō (a retainer of Kagetora) in the sixth month of 1549, Sadamitsu claimed that he was the subject of deceptive tactics and threats from Masakage, did not have power himself, and his retainers suffered from low morale so if preparations for defense were delegated solely to them, there would be regrets later on.
Sadamitsu temporarily left Kagetora, but later returned and, in the first month of 1551, clashed with Hatchi Nagayoshi and Anazawa Nagakatsu. Around summertime in the same year, it appears that a dispute arose between Sadamitsu and Magotarō in regard to the former territory of Tagō Kosaburō. Magotarō, along with magistrates of Kagetora including Ōkuma Tomohide, Naoe Kagetsuna, and Honjō Saneyori appealed for a judgment whereupon there was no increase to his fief and the retainers lost their zeal to fight.
Later, after resolution of the dispute between Kagetora and Masakage, Sadamitsu’s name disappears from authenticated sources. It is surmised that Sadamitsu did not have an important role under Kagetora and the Usami family declined. The family, however, was not extinguished. In the eighth month of Eiroku 10 (1567), an individual named Usami Heihachirō is noted among those who prepared defenses against the invasion of Shinano Province by Takeda Shingen.
Sadamitsu’s presence in Biwajima Castle
In military accounts written in the Edo period, Usami Sadayuki is named as the lord of Miwajima Castle while Sadamitsu is also introduced in many works as the lord of Biwajima Castle. The presence of Sadamitsu’s father, Usami Fusatada, at Biwajima Castle is substantiated, but the subsequent relationship between the Usami clan and Biwajima Castle cannot be clearly confirmed from authenticated sources.
Questions regarding the identity of Lord Biwajima
In the era of Uesugi Kagetora, the individual surmised to be the lord of Biwajima Castle is referred to in one account from 1559 as Lord Biwajima of the Hirō-tachi group. In military service records of the Uesugi family from 1575, he is named as Lord Yashichirō, and, in other records of the Uesugi family from 1577, as Biwajima-Yashichirō. The Uesugi family genealogy from 1559 treats Sadamitsu as a separate individual from Biwajima-Yashichirō. Certain researchers interpret Lord Biwajima to be Usami Sadamitsu, but uncertainties remain. Other historical accounts from 1575 refer to Biwajima-Yashichirō, but this may refer to Nagao Kagemichi. Yashichirō was also the childhood name of Sadamitsu’s father, Fusatada, so it is possible that Sadamitsu’s son or grandson received the same childhood name. Moreover, adoption of the Biwajima name owes to having a residence at Biwajima Castle.
In the first half of the sixteenth century, the Usami clan was based at the stronghold of Ono Castle, and the Kakizaki were members of the Usami family, so the homeland of the Usami clan is surmised to have been in the present-day area of Kakizaki.