Lifespan: Tenbun 3 (1534) to 3/6 of Tenshō 10 (1582)
Other Names: Matabei
Title: Governor of Bungo
Lord: Takeda Shingen → Takeda Katsuyori
Father: Obata Toramori
Wife: Daughter of Hara Toratane
Children: Masatada, Arinao, Kagenori, Masashige
Obata Masamori served as a bushō during the Sengoku period. As a retainer of the Kai-Takeda clan, Masamori served Takeda Harunobu (Shingen) and Takeda Katsuyori. He was a general of the ashigaru, or foot soldiers, and is counted among the Twenty-Four Generals of the Takeda.
The Obata clan originated from Katsumada in Tōtōmi Province. In the era of his grandfather, Obata Nichijō (Moritsugu), and his father, Obata Toramori, the family visited Kai Province and was engaged in service by Takeda Nobutora, a sengoku daimyō and the eighteenth head of the Kai-Takeda clan. Toramori was stationed at Kaizu Castle (later known as Matsushiro Castle) located on the front lines of northern Shinano in an area contested by Uesugi Kenshin of Echigo Province. He served as an assistant to Kasuga Toratsuna. According to another account, Masamori and Toramori were stationed at Kaizu Castle. Toramori died in the sixth month of 1561 before the Fourth Battle of Kawanakajima. Masamori then inherited the headship of the clan and was ordered to continue to support Toratsuna.
In the eleventh month of 1561, Masamori served in the Fourth Battle of Kawanakajima, and then as a general inspector for western Kōzuke under the command of Naitō Masatoyo (Masahide). After arranging for Masamori to wed as his formal wife the daughter of Hara Toratane, Shingen said “The daughter of a demon is appropriate for the son of a demon.” Toratane was also a general of the ashigaru. According to one account, following the demise of Toramori, Masamori was endorsed as the lieutenant general of Kaizu Castle, but owing to his desire to serve as a hatamoto, or retainer, of Shingen, he raised a claim instead. This upset Shingen whereupon Masamori was confined to the Myōon Temple in Kōfu and ordered to commit seppuku. Nevertheless, after urgent appeals from Suwa Katsuyori and Tsuchiya Masatsugu, Masamori was pardoned and remained a general of the ashigaru.
His name appears in records once with Nagasaka Masakuni as magistrates for prayers organized to supervise monks in the territory in the eleventh month of 1571.
In 1582, during the era of Katsuyori, the allied forces of Oda Nobunaga and Tokugawa Ieyasu invaded the territory of the Takeda. This is known as the Conquest of Kōshū. Owing to illness, Masamori could not participate in the defense. As prospects of defeat deepened, Katsuyori escaped to the Kaizenkō Temple where Masamori said his final goodbye and later died of illness. He was forty-nine years old. According to the description in one account, his death is interpreted to have been due to an endemic illness known as bilharzia, indicating that this may have been prevalent in Kai Province during this period.
Until the era of Toramasa, the family used the Obata surname written as 小畠, but, from the era of Masamori, adopted the characters written as 小幡. Masamori’s third son, Masamori Kagenori, is well-known for authoring the Kōyō-gunkan, a compilation of military strategies and tactics of the Takeda clan created in the early Edo period.