However, it is documented that when the Retired Emperor Gotoba raised an army to overthrow the Shogunate, Mototsuna took part in the Retired Emperor's side, and that when it was defeated, he was killed and his severed head was exposed (the article of July 18, 1221 in "Azuma Kagami" [The Mirror of the East]).
が、承久3年（1221年）に後鳥羽上皇が倒幕の兵を挙げると基綱は上皇方として参加し、その敗北とともに討ち取られ梟首されたとの記録が残る（『吾妻鏡』同6月20日(旧暦)条）。