This was because the eldest son of Odai no kata, Yasumoto was always away from home and her second son Katsutoshi had been held hostage by another family since he was a child.
それは、於大の方の子たちで、長兄・康元が常に本国を留守にし、また次兄・勝俊も、少年時代から他家へ人質として出されていた為であった。