Sōma clan
Yoshitane was the eldest son of Sōma Moritane, the 15th chieftain of the Sōma clan. At the time, the clan was based at Odaka Castle. In 1559, the clan was approached by Date Tanemune and was offered a matrimonial alliance. Yoshitane was wed to Tanemune's younger daughter, Kosugō Gozen the following year. However, following the death of Tanemune in 1565, the ancient enmity between the Sōma and Date clans flared up again in a border dispute, and Yoshitane divorced Kosugō Gozen and sent her back to the Date clan.