Though I Am An Inept Villainess v.1
As the crown prince's favored maiden at court, Kou Reirin's future as the next empress is all but assured. That is, until her rival Shu Keigetsu, the court's "sewer rat," pushes her over a balcony! Reirin survives but wakes up in Keigetsu's body! Turns out, Keigetsu has used magic to swap bodies with Reirin in order to steal her position at court.
After being sickly her whole life, Reirin is determined to use this new body to turn things around. She won't let anything stop her, not even her impending execution!