Imagawa clan
During the Imagawa clan succession crisis in 1476, Shinkurō whose sister was married to Imagawa Yoshitada, Shugo (Governor) of Suruga province, became associated with the Imagawa clan. At the death of Yoshitada in battle, Shinkurō went down to Suruga province to support his nephew Imagawa Ujichika. Through this relationship Shinkurō quickly established a base of power in Kantō.