The Queen Mother is king Ei Sei's mother and the leader of the Royal Harem faction.

In the past, she was known as the "Jewel of Kantan" for her amazing beauty. At that time she was Ryo Fui's fiance and was deeply in love with him. Ryo Fui gave her to Sei's father to become one of his many women in order to gain from this arrangement in the future.

She became a political hostage together with Sei in the State of Zhao and she gave birth to him there. During that time she and Sei would suffer tremendous hardship under the people of Zhao and, due to that, she grew to hate Sei and even attempted to kill him at some point.

After Sei successfully escaped from Zhao at the age of eight and became the king of Qin, the queen mother was brought to the capital as well and became the head of the Royal Harem.

(Source: Kingdom Wikia)