also known as was one of Takeda Shingen

Takeda Shingen

, of Kai Province, was a preeminent daimyo in feudal Japan with exceptional military prestige in the late stage of the Sengoku period.-Name:Shingen was called "Tarō" or "Katsuchiyo" during his childhood...

's most loyal retainers, and one of his "Twenty-Four Generals

Twenty-Four Generals of Takeda Shingen

The Twenty-Four Generals were just one of many historically famous groupings of battle commanders from Japan's Sengoku Period. These Twenty-Four were the most trusted commanders of the armies of Takeda Shingen...

" during the Sengoku period

Sengoku period

The or Warring States period in Japanese history was a time of social upheaval, political intrigue, and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. The name "Sengoku" was adopted by Japanese historians in reference...

 of Japan. He is often credited as the original author of Kōyō Gunkan

Koyo Gunkan

The ' is a record of the military exploits of the Takeda family, compiled largely by the Takeda vassal Kōsaka Danjō Masanobu, and completed in 1616 by Obata Kagenori...

, which records the history of the Takeda family

Takeda family

The ' was a famous clan of daimyō in Japan's late Heian Period to Sengoku period.The Takeda were descendants of Emperor Seiwa and are a branch of the Minamoto clan , by Minamoto no Yoshimitsu , brother to the Chinjufu-shogun Minamoto no Yoshiie...

 and their military tactics. However, recent studies strongly suggest that other writers used Kōsaka's name to boost the book's credibility.

Bond with Shingen

The association between Masanobu and Shingen began in 1543 as a love relationship. At the time they were 16 and 22, respectively. Such relationships were in vogue in pre-modern Japan, a tradition known as shudo. The love pact signed by the two, in University of Tokyo

University of Tokyo

, abbreviated as , is a major research university located in Tokyo, Japan. The University has 10 faculties with a total of around 30,000 students, 2,100 of whom are foreign. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is considered to be the most prestigious university...

's Historical Archive, documents Shingen's pledge that he was not in, 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)

Commander

Kōsaka is known as one of the three Danjō that served the Takeda family, along with Sanada Yukitaka

Sanada Yukitaka

was a daimyō of Shinano Province who became one of Takeda Shingen's 'Twenty-four Generals' , submitting to become Takeda's vassal after a long and difficult struggle against him....

 and Hoshina Masatoshi

Hoshina Masatoshi

' was a Japanese samurai of the Sengoku period, who served the Takeda clan. The son of Hoshina Masanori, he ruled Takatō Castle in Shinano Province. He initially opposed Takeda Shingen's invasion of Shinano; however, he later submitted to Shingen and became a Takeda vassal, in command of 120...

 (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

Battles of Kawanakajima

The ' were fought in the Sengoku Period of Japan between Takeda Shingen of Kai Province and Uesugi Kenshin of Echigo Province in the plain of Kawanakajima, in the north of Shinano Province. The location is in the southern part of the present-day city of Nagano.The five major battles took place in...

. He informed Takeda via signal fires of the movements of Uesugi Kenshin

Uesugi Kenshin

was a daimyo who ruled Echigo province in the Sengoku period of Japan.He was one of the most powerful lords of the Sengoku period. While chiefly remembered for his prowess on the battlefield, Kenshin is also regarded as an extremely skillful administrator who fostered the growth of local industries...

'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, turning the tide of the battle into a Takeda victory.

Retirement and death

Kōsaka Masanobu is known to have openly criticized Katsuyori

Takeda Katsuyori

was a Japanese daimyo of the Sengoku Period, who was famed as the head of the Takeda clan and the successor to the legendary warlord Takeda Shingen. He was the son of Shingen by the , the daughter of Suwa Yorishige...

 numerous times. Because of this, Kosaka was forced to "retire" from service in 1578 and died later from illness.

In culture

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

Kabuto

A kabuto is a helmet used with traditional Japanese armour as worn by the samurai class and their retainers in feudal Japan....

 helmet with a menpō

Menpo

A is one of several types of facial armour worn by the samurai class in feudal Japan...

.