The Twelve Kingdoms Wiki

Joei (舒栄) is the younger sister of the previous queen of Kei, Jokaku, daughter of the Jou family. Unlike her sister, she is confident and believes herself to be qualified to be a monarch; as a result, she resents that Jokaku was chosen to be the queen instead. When Jokaku became increasingly withdrawn, Joei encouraged this attitude and took advantage of her sister's affection for her in order to gain power within the court. When Jokaku dies, Joei attempts to take control of Kei as its new monarch while Keiki disappeared from Kei in order to find the next king of Kei.

Because she was not chosen by Keiki, Joei is not the true ruler of Kei and unable to enter the royal palace at Gyouten and is forced to take up residence in the palace of the governor of Sei Province. Her claim to the throne is augmented by the machinations of the king of Kou, who arranges for his kirin, Kourin, to capture and enchant Keiki so that he is unable to speak and convince the people of Kei that Joei is the new ruler. Her possession of Keiki is enough to convince any remaining provincial governors doubting her legitimacy to support her, with the exception of Koukan, the governor of the Baku Province.

Aided by the king of En, the true ruler of Kei, Youko Nakajima, is able to overthrow the false queen and Joei is ousted from Kei.