I think the swallow turned into Princess Zhu Huan by relying on her own fate and the love of the emperor. At first, Swallow met Wei Zi. She wanted to go to Beijing to recognize her father. It was luck that she and Wei Zi became good sisters, and then there was an incident of admitting their mistakes. But because both the emperor and Mei loved her very much, what she replaced went away. Later, the swallow became a real princess recognized by the emperor.