Perhaps because of his mother's low birth, he was not chosen to be the successor to the Ononomiya family, so in 989, at the age of seven, he was entrusted to the care of the Tendai-sect priest Keien (Kyoen) of Enryaku-ji Temple (who was also Sanesuke's maternal uncle).
母親の出自によるものか、小野宮家の後継者とはみなされておらず、永祚(日本)元年（989年）に7歳にして延暦寺の慶円(天台宗)（実資の母方伯父）の元に預けられた。