One of the Takeda Four Generals. A wise general known for avoiding reckless battles and executing brilliant retreats, earning the nickname "The Retreating Magistrate." At the Fourth Battle of Kawanakajima, he commanded the detached force striking the Uesugi rear. He is also credited as the original author of the Koyo Gunkan, which recorded Shingen's strategies and passed Takeda tactics to later generations.

A rational strategist who saw no shame in retreat, seeking maximum results with minimum casualties. Shingen praised him saying "Kosaka's retreats are worth ten thousand soldiers."

Renowned as "The Retreating Magistrate," he is highly regarded in later military scholarship. He left his mark in history as a general of both sword and pen, transmitting Takeda tactics to posterity through the Koyo Gunkan.