Kōsaka Masanobu

Kōsaka Masanobu (高坂昌信) (b. 1527 d. 1578) was one of Takeda Shingen's most loyal retainers, and one of his 'Twenty-Four Generals' during the Sengoku period of Japan. He is often credited as the original author of Kōyō Gunkan, which records the history of the Takeda family and their military tactics. However, recent studies strongly suggest that other writers used Kōsaka's name to boost the book's credibility.

The association between Masanobu and Shingen began in 1543 as a love relationship. At the time they were sixteen and twenty two, respectively. Such relationships were in vogue in pre-modern Japan, a tradition known as shudo. The love pact signed by the two, in Tokyo University's Historical Archive, documents Shingen's pledge that he was not, nor had any intentions of entering into, a sexual relationship with a certain other retainer, and asserts that "since I want to be intimate with you" he will in no way harm the boy, and calls upon the gods to be his guarantors. (Leupp, pp. 53–54)

Kōsaka is known as one of the three Danjō that served the Takeda family, along with Sanada Yukitaka and Hoshina Masatoshi (Danjō stands for a formal title, Danjōchū; 弾正忠). Among these three, Kōsaka was known as the "Nige Danjō" (literally, the fleeing Danjō), because of his cautious commanding and skillful retreats.

As the general in command of Kaizu castle, Kōsaka played an important role in the fourth Battle of Kawanakajima. He informed Takeda via signal fires of the movements of Uesugi Kenshin's army as it approached, and then led the sneak attack up Saijo-yama in order to drive Uesugi's men down to the plain where they could be surprised by Takeda's army. Even though that tactic failed, Kōsaka led his men back down the hill, attacking Uesugi's army from the rear, and turning the tide of the battle into a Takeda victory.

Kōsaka Masanobu is known to have openly criticized Katsuyori numerous times. Because of this, Kosaka was forced to "retire" from service in 1578 and died later from illness.

In popular culture, especially in video games, Kōsaka Masanobu is often seen wearing a full kabuto helmet with a menpō.