However, once the Heian period started, the blood or marriage relationship with Emperor was ignored due to the complicated succession to the Imperial Throne caused by the abdication of several Emperors, which constantly led to elevate the lower position of a woman to "Koi" in the changing of Emperor and also to appoint who was "Koi" on the grounds of political background.
しかし、平安時代に入ると、譲位による皇位継承の複雑化に伴い、天皇の交代に伴う后位の引き上げや政治的な背景による后位の決定が恒常化し、天皇の血縁や配偶関係は無視された。