He was Jidoku (Imperial Tutor) throughout the two-emperor eras of Montoku and Seiwa, and even today, there remain many Imperial edicts and Ganmon (Imperial prayer documents for a blessing) which Koreyoshi drafted as Naiki (the Secretary of the Ministry of Central Affairs).
文徳天皇・清和天皇両天皇の侍読となり、内記として起草した詔勅や願文が多く残されている。