Yanagimoto Jinjirō served as a bushō during the Sengoku period. He was a retainer of Hosokawa Harumoto. Jinjirō also served as the lord of Sanjō Castle in Kyōto.
Yanagimoto Kataharu, the head of the Yanagimoto clan, cooperated with Hosokawa Harumoto to defeat Hosokawa Takakuni. Kataharu became a member of Harumoto’s newly established administration, but he often conflicted with Miyoshi Motonaga. Kataharu was assassinated in the midst of a battle against Uragami Muramune. At the time of Kataharu’s demise, his son, Toramitsumaru, was still young so Jinjirō succeeded Kataharu as a proxy for Toramitsumaru, becoming the head of the clan.
After killing Takakuni in a battle known as the Collapse at Daimotsu, Motonaga came into conflict with retainers of Harumoto including Kizawa Nagamasa. Early in 1532, he led forces against Jinjirō at his home base of Sanjō Castle in Kyōto. The castle fell while Jinjirō perished in the battle to forces from Awa led by Motonaga.
The killing of Jinjirō raised tensions between Motonaga and Harumoto. Hosokawa Mochitaka of the Awa-Hosokawa family served as a mediator. A settlement was reached after Motonaga and his retainer underwent the rites of tonsure to demonstrate their allegiance. Thereafter, Mochitaka severed ties with Harumoto and returned to Awa. The confrontation flared again, whereupon Harumoto killed Motonaga.