Tsunehiro was a son of Yonehara Heinaizaemon. He first served Amako Haruhisa and received Takase castle in 1562. He later betrayed the Amako and joined the Môri, fighting against his former masters at Gassan-Toda in 1564-66. At that time he clashed with the forces of his own father-in-law, Amako general Sase Kiyomune. Tsunahiro was later asked to join the forces under Amako Katsuhisa then preparing to make a bid to recapture Gassan-Toda. He gave his tacit acceptance but when the Amako and Môri clashed between 1569-1570, he sat on the fence waiting to see what the prospects for success were. Nonetheless, the Môri turned on Takase after defeating Katsuhisa's army at Nunobeyama and put it under siege. Tsunahiro escaped the castle and made his way to Kyoto, where he lived in retirement until his death.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005