An Xiaoqing, who likes reading novels, accidentally traveled to the home of a general from an unknown dynasty and possessed the body of his twin sister, Shangguan Qing'er. His brother Shangguan Yujin got along with the sister who had changed her personality and found that he fell in love with her. But how would An Xiaoqing, who had studied biology, choose this love in a dynasty where he could not get married without close relatives?