Koushaku Reijou Theresia no Fukushuu: Akuma no Chikara, Okarishimasu

A young woman named Tiaresia, the daughter of a duke, is preparing for her entrance into high society. She is accompanied by a devoted servant who becomes increasingly restless. This servant is, in fact, a demon bound by a magical agreement with Tiaresia, who is the reborn version of Queen Kristian. Kristian had been wrongly accused by her half-sister and executed at sixteen. Now, two decades later, she and the demon devise a plan for a precise and sorrowful vengeance.