Morikuni was descendant of samurai who served on retired Emperor Gotoba's Northern flank during the Kamakura period served and Nishina Morito who fought on the imperial side in 1221 during the Jokyu War.
鎌倉時代に後鳥羽上皇の北面の武士となり1221年（承久3年）の承久の乱の時に朝廷方に付いた仁科盛遠の末裔。