Imagawa clan
Shinkuro became a retainer in the Imagawa clan, and when Yoshitada died in battle in 1476, Shinkurō mediated the succession dispute between supporters of Yoshitada's son Imagawa Ujichika and Yoshitada's cousin, Oshika Norimitsu. This proved a temporary peace. When Norimitsu again attempted to gain control of the Imagawa clan, Sōun came to Ujichika's defense, killing Norimitsu. Sōun was rewarded by Ujichika with Kōkokuji Castle.