Futsutsuka na Akujo dewa Gozaimasu ga: Suuguu Chouso Torikae Den

In the Kingdom of Ei, the Maiden Court is the place where chosen women from powerful families compete to become the future empress. Reirin Kou is a graceful and respected lady who is kind to everyone and becomes their favorite. However, she has one weakness: she often gets weak and remains sick most of the time. 

There was another candidate, Keigetsu Shu is a rough and tough lady who is always jealous of Reirin’s life. During a rare Comet event, Keigetsu tries to kill Reirin by pushing her from a balcony. Before anyone saw them, she used her magic and replaced Reirin’s body with hers. By doing this, Reirin gets the healthy body of Keigetsu and enjoys her new life while Keigetsu struggles with Reirin’s weak body.