Yasutoki was welcomed to Kamakura from Kyoto as the new lord of Kamakura after the assassination of the third shogun, Sanetomo MINAMOTO, and he caused Mitsutora, who was eight years old, to celebrate his coming of age and take the name Yoritsune FUJIWARA.
3代将軍源実朝暗殺後に新たな鎌倉殿として京から迎えられ、8歳となっていた三寅を元服させ、藤原頼経と名乗らせた。