Given the situation, FUJIWARA no Yoshifusa started to enhance his political power during Emperor Nimmyo's reign; he let his grandchild, his fourth prince, Korehito (later called Emperor Seiwa), whose mother was Some dono no kisaki (Empress) FUJIWARA no Akirakeiko (Empress Some dono) (Akira Keiko) become the crown prince, married while the Emperor was the crown prince, and finally had Prince Korehito in the same year as the Emperor's enthronement.
こうした経緯も含め、藤原良房は仁明朝期頃から次第に権勢を強め、文徳天皇が東宮だった頃に嫁がせていた娘、染殿后藤原明子(染殿后)（あきらけいこ）がちょうど天皇即位の年にようやく産んだ、第四皇子惟仁親王（のちの清和天皇）を立太子させる。