Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 16 - 16-68. Saga Empire, Battle at the Imperial Capital (1)

I freed the Slaves, but for some reason, they keep chasing after me.

After being betrayed by her fiancé and her cousin sister, she accidentally rescued an elegant but indifferent young master. Never did she expect to marry him and surprised many!

Beings that create and control monsters and demons, beings that build and reign over malicious labyrinths, the chosen individuals to possess an overwhelming Unique Skill… They are the Demon Lords.

Yao Mo Xin, the empress of Da Chu died in a cruel way a day after she gave birth at the hands of her husband the emperor, Ye Hong Yi, and her legitimate second sister, Yao Shu Ran. Ye Hong Yi got the throne because of the smartness of Yao Mo Xin, but he hated her because she made him feel like a useless person who needed a woman to become the emperor.

Her soul got in the body of her illegitimate third sister from the same mother Yao Mo Wan. Yao Mo Wan has the mentality of a child because the legitimate wife of her father fed poison to her mother while she was carrying Yao Mo Wan. Yao Mo Xin wants revenge for everything that happened to her, so she seduced the emperor and began her plan of taking everything away from him. She did that while pretending to still have the mentality of a child. She also wants to repay Ye Jun Qing back for everything he did for her while she was Yao Mo Xin. In the process of revenge, she met many people who will fall in love with her wit and intelligence.

- Description from Novelupdates