His father Hideyoshi Sasaki fought against the Taira clan in the Hōgen (1156) and Heiji Wars (1160).
Shigekuni's longtime kindness made Hideyoshi unable to make up his mind.
His son Yoshikiyo also worried about the same problem, but he decided to side with the Taira clan finally.
Yoshikiyo, who was on the Tairas' side, won the Battle of Ishibashiyama, which turned out to be the first fight of a series of wars.
After the war ended, his four elder half-brothers were praised for their distinguished military services by Yoritomo, and they got their own feudal estates.