Ingo, which was originally conferred on only the Emperor and three Empresses: the Empress, the Empress Dowager and the Grand Empress Dowager, began being conferred among subjects when the chief adviser to the Emperor, FUJIWARA no Kaneie called himself as Hokoin.
もとは天皇、三后のみに許されていた院号が、臣下にも普及するようになったのは、関白藤原兼家が法興院を称したことによる。