In the article of August 27, 1186, the day of the Kanoto Ushi in the Sexagenary Cycle, the author of "Azuma Kagami" (The Mirror of the East) wrote as follows: 'the governor of Tosa Province Kunimoto is a member of the family of the nihon (MINAMOTO no Yoritomo). The friendship between the two was especially strong to the extent that the emotion can cut through a piece of metal.'
『吾妻鏡』文治2年(1186年)8月27日辛丑の条に「土佐国守国基は二品（源頼朝）の御一族なり。殊に断金の契約有り」と記されている。