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He was the eldest son of Haruhisa and he and was given the childhood name of saburōshirō (三郎四郎?). After his father's sudden death on 1560, he became the head of the clan to continue the fight against the Mōri clan. While besieged in Toda Castle, Yoshihisa had a retainer, Moriyama Hisakane executed after fearing a betrayal. This caused most of his remaining troops to desert and on 1566, he surrendered to Mōri Motonari. Yoshihisa was granted of a wish to become a monk and was held in captive at Enmeiji. With the head of clan gone, the Amago clan was forced to serve as retainers to other daimyo.
Yoshihisa's monk name is Yurin(友林) and after Mōri Terumoto became the head of Mōri clan, he became a retainer under Terumoto.