On August 6, 1180, Moritsuna was ordered to come to a private room of Yoritomo who made up his mind to defeat the Taira clan, and was told about a plan to raise an army.
治承4年（1180年）8月6日、平氏打倒を決意した頼朝の私室に一人呼ばれ、挙兵の計画を告げられる。