Kōsaka Masanobu (高坂 昌信) also known as Kasuga Toratsuna (春日 虎綱, 1527 – June 12, 1578) was a Japanese samurai warrior of the Sengoku period.

In 1561, as the general in command of Kaizu castle, Kōsaka played an important role in the fourth Battle of Kawanakajima.

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.

[4] In 1575, he led troops to protect Takeda Katsuyori's rearguard at Battle of Nagashino when the latter had been forced to retreat by the Oda-Tokugawa alliance.

The love pact signed by the two, in University of Tokyo'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.