Born the fourth son of Tadatoshi, who served as Sangi (Councilor) of the Imperial government, FUJIWARA no Sanesuke was later adopted by his grandfather, Saneyori, as his son; and adored by Saneyori, he inherited the bulk of Saneyori's family territory, succeeding Saneyori as the head of the house of Ononomiya.
実資は参議斉敏の四男に生まれ、後に祖父の実頼の養子となり、非常に愛されて家領の多くを相続し、小野宮流を継承する。