Eiki was Sa Enjun's consort, who remained in the Sa Province to act as the clan head while he carried out his duties as Taiho in the imperial capital. Despite being separated for much of their long marriage, they fell deeply in love and eventually married. After Enjun's death, his ambitious younger brother Chuusho imprisoned Eiki and Shunki.
Eiki was born into the Hyou clan, a mysterious shadow lineage within Saiunkoku. Although she would not have typically married outside her family, she fell in love with Enjun and pursued him until he agreed to marry her. As a member of the Hyou clan, Eiki possessed supernatural powers such as precognition, which turned her against Advisor Sho because she always knew that he would be involved in Enjun's death. Additionally, she sealed off the powers and voice of their granddaughter Shunki during her childhood.