According to Azuma-kagami (history book), MINAMOTO no Yoritomo wrote in his letter to his younger brother, MINAMOTO no Noriyori, just before the Battle of Danno-ura: "As Naifu (Munemori) is such a cowardly person, I cannot imagine that he would dare commit suicide."
『吾妻鏡』によると源頼朝は壇ノ浦の戦いの直前、弟の源範頼に宛てた書状で、「内府は極めて臆病におはせる人なれば、自害などはよもせられじ」と記している。