Due to the defeat of MINAMOTO no Yoshitomo whom Morituna's father followed in the Heiji War in 1159, Hidetsuna (name of Moritsuna before Genpuku (coming-of-age ceremony)) escaped to the Kanto region with his family and was protected by Shigekuni SHIBUYA.
平治元年（1159年）の平治の乱で父が従った源義朝の敗北により、一門と共に関東へと落ち延び、渋谷重国の庇護を受ける。