The Emperor is the lavishly adorned ruler of Sei-an City who has such a love of gold that even his eyes are covered by gold coins. His special fondness though is for demon fangs, claiming each has slight variations and has made it his hobby to one day obtain them all.
The Emperor had suddenly fallen ill, unknowingly possessed by Blight who had spread a toxic mist across Sei-an City, sickening its people. He had Kaguya jailed with no given reason and sealed away Kasugami. After Blight has been removed from his body he frees Kaguya and seems to have no memory of the events but welcomes the white wolf Amaterasu into his palace believing her to be lucky.
The Emperor and Queen Himiko each have their own places with Himiko’s being exceptionally larger than the Emperor’s with equally elaborate security measures. The Emperor and Queen Himiko never acknowledge one another’s existence and Himiko seems to be the one in charge while the Emperor acts merely as a decoration.