Emperor Kōnin
Upon the death of Empress Shōtoku in 770, Yakatsugu aligned with Fujiwara no Nagate in supporting the future Emperor Kōnin as her successor. The appreciative new emperor continued to value him, and Yakatsugu was promoted to "chūnagon" in 771 and "dainagon" in 780, making him the third highest ranking figure in the "daijō-kan" after "udaijin" Ōnakatomi no Kiyomaro and "naidaijin" Fujiwara no Uona. During this period, he also held positions as head of the Dazaifu, "shikibu-sho", Ministry of the Center, and Crown Prince's Quarters. In 775, he reclaimed his family's old name of Mononobe no Ason, but in 779 he changed it back to Isonokami, now as .