Ishikawa Kazumasa (1534–1609) was a prominent Japanese retainer who began serving Tokugawa Ieyasu during his youth. Their relationship began in 1551 when both were hostages under the Imagawa clan. Kazumasa remained a loyal companion to Ieyasu, participating in key events such as the Siege of Terabe in 1558 and the Siege of Marune in 1560. After Ieyasu broke away from the Imagawa following the latter event, Kazumasa became a trusted retainer and administrator in his service.
In 1562, during the Siege of Kaminogo Castle, Kazumasa played a crucial role as Ieyasu successfully negotiated the release of his family from Imagawa Ujizane. Acting as their guardian, Kazumasa undertook this perilous duty with great responsibility. By 1567, Tokugawa forces were divided into two major divisions. Kazumasa was appointed commander of 13 Tokugawa daimyo-vassals, while Sakai Tadatsugu oversaw 18 daimyo-vassals.
Kazumasa fought in several critical battles, including the Battle of Mikatagahara in 1573 and the Battle of Nagashino in 1575. Following Toyotomi Hideyoshi's victory over Shibata Katsuie in 1583, Ieyasu conveyed his congratulations through Kazumasa. However, under Tokugawa orders, Kazumasa and Sakakibara Yasumasa later issued statements denouncing Hideyoshi. Kazumasa served at the Tokugawa headquarters in Komaki during the Komaki-Nagakute Campaign of 1584.
In 1585, Kazumasa became increasingly disillusioned with Ieyasu's defiance of Hideyoshi. Viewing this resistance as reckless, he defected to Hideyoshi’s side. This betrayal forced Ieyasu to overhaul his military organization and defense strategies, as Kazumasa had deep insights into Tokugawa operations.
After Hideyoshi's death and the establishment of the Tokugawa Shogunate, Kazumasa and his family faced punitive measures, losing their fief. Kazumasa eventually retired and spent his remaining years with his son, Ishikawa Yasunaga, until his death in 1609.
See also
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Otomo Sorin
Ōtomo Yoshishige came from a noble lineage, being the eldest son of Ōtomo Yoshiaki, the ruler of Funai Province. The roots of the Ōtomo family traced back to Fujiwara Hidesato, the adopted son of Nakahara Chikayoshi. Fujiwara served Minamoto Yoritomo during the Genpei War and took part in battles in Mutsu Province in 1189. In 1193, he was appointed shugo of Buzen and Bungo Provinces, after which he adopted a new surname—Ōtomo.
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Okudaira Sadamasa
Sadamasa was the son of Okudaira Sadayoshi and took part in several battles under Tokugawa Ieyasu, distinguishing himself in the Battle of Anegawa in 1570, where he took two heads. Around 1572 he was forced to enter the service of the Takeda clan, but after the death of Takeda Shingen in 1573 he returned to Tokugawa, leaving Tsukude Castle together with his men. As a result of this defection, Takeda Katsuyori ordered the execution of Sadamasa’s wife and brother, who were being held as hostages.
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Okubo Tadatika
Tadatika, the son of Okubo Tadayō, entered the service of Tokugawa Ieyasu at the age of eleven, and took his first head in battle when he was sixteen. After the establishment of the Tokugawa shogunate, he was appointed as a rōjū — a senior bakufu official — and was regarded as one of Ieyasu’s most trusted advisors, alongside Honda Masanobu. He is also known for his military chronicle Mikawa Monogatari, which describes Ieyasu’s rise to power and the early years of the Tokugawa shogunate.
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Okubo Nagayasu
Nagayasu was the second son of Okura Nobuyasu, a sarugaku theater actor from the Takeda clan. Takeda Shingen recognized the young man’s potential and took him into service, appointing him as a vassal to his general, Tsuchiya Masatsugu. During this period, Nagayasu changed his family name to Tsuchiya. He was entrusted with developing the Takeda clan’s gold mines as well as handling matters related to taxation.
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Nitta Yoshisada
Nitta Yoshisada was a loyal soldier of Emperor Go-Daigo, who in the 1330s attempted to restore direct imperial rule in Japan. The Nitta family was related to the Ashikaga house and was older in lineage. However, they did not join Minamoto Yoritomo at the start of his war with the Taira, as the Ashikaga did, and therefore did not receive high positions in the Kamakura shogunate. This may have been one of the reasons why Yoshisada rose against the Hōjō clan in 1333.
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Natsume Yoshinobu
Yoshinobu, a long-time vassal of the Matsudaira and Tokugawa clans, governed Hamamatsu Castle on behalf of the Tokugawa house. During the clashes between the Imagawa, Takeda, and Matsudaira clans, he served in the garrison of Nagasawa Castle and in 1562 took part in raids under the command of Itakura Shigezane. When, in 1563, a revolt of the Sōtō-shū sect followers broke out in Mikawa Province, Yoshinobu joined the rebels together with Honda Masanobu and Hachiya Sadatsugu.
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Nambu Nobunao
The Nambu clan was an ancient and powerful family that traced its lineage back to the Minamoto shoguns and had controlled a significant part of the Tohoku region in northern Honshu since the 12th century. Nobunao was born in Ikatai Castle, located in what is now the city of Iwate. He was the second son of Ishikawa (Nambu) Takanobu, the 22nd head of the Nambu clan. In 1565, Nobunao’s uncle, Nambu Harumasa, adopted him, brought him to Sannohe Castle, and named him his heir, later giving his daughter in marriage to him.
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Naito Ienaga
Ienaga was the son of Naitō Kiyonaga and served Tokugawa Ieyasu from an early age. Like his father, he was exceptionally brave, and thanks to his remarkable skill with the bow, he earned the nickname “the unrivaled archer.” Although both the elder and the younger Naitō belonged to the Jōdo Shinshū (“True Pure Land”) sect, during the Ikkō-ikki uprising in Mikawa Province in 1565, Ienaga did not support his fellow believers and instead sided with Tokugawa Ieyasu, earning his special trust. He later took part in the battles of Mikatagahara, Nagashino, and many other engagements while accompanying Ieyasu.
