When he divorced his wife who was the adopted daughter of Yoshioki OUCHI, and remarried the daughter of Hisayuki AMAGO, a younger brother of Tsunehisa AMAGO, Motoshige defected from the Ouchi clan with the support of the Amago clan of Izumo Province as a backdrop.
大内義興の養女である妻を離縁し、尼子経久の弟尼子久幸の娘を妻とすると、出雲国尼子氏の支援を背景に大内氏を離反した。