He also earned Michinaga's trust to the point that when Michinaga became seriously ill, he called Yukinari to ask him to be Koken (guardian) of his legitimate son Tsuru gimi (Yorimichi）.
また、道長が病気で一時重態になった際には行成を呼んで嫡男鶴君（頼通）の後見を依頼する程の信頼を得ていた。