Kusuri de Osanaku Natta Okage de Reikoku Koushaku-sama ni Hirowaremashita

Cherise, who is the country's saint if only in name, is falsely accused of a conspiracy by her step-sister, Aria, and is exiled from her country. She flees for her life—until, when faced with a life or death situation, she consumes the potion given to her by His Majesty, and to her surprise, her body changes into that of a young girl! She is then confronted by Diaz, who is rumored to be a "ruthless duke."