Ujimoto was a son of Katsurayama Ujihiro. He was at first a vassal of the Imagawa and held Katsurayama castle in Suruga province. He joined the Takeda when Takeda Shingen invaded the Imagawa's domain in 1569. He evidently had a secret understanding with Shingen prior to the Takeda invasion and he afterwards adopted one of Shingen's sons, Takeda Nobusada (also known as Katsutoshi).
- Initial text from Samurai-Archives.com FWSeal & CEWest, 2005