 Kuniyoshi was the 7th son of Ishikawa Yoshimitsu, the 13th hereditary chieftain of the Ishikawa clan, a cadet branch of the Date clan of Sendai Domain.In 1863, Tamura Yukiaki, the 9th "daimyō" of Ichinoseki Domain was adopted by Date Yoshikuni as heir apparent to Sendai Domain, which left Ichinoseki Domain leaderless.Kuniyoshi was appointed by clan elders to become "daimyō" and became the adopted son of Yukiaki through marriage to Yukiaki's daughter.