Sadatsuna originally served the Imagawa and was known as Okabe Chûbei. He joined Takeda Shingen and adopted the name by which he is better known. He was something of a naval commander and had 12 vessels under his control, though he would be killed fighting on the ground at Nagashino in 1575.
References
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005