Munou Saijo wa Akujo ni Naritai: Gimai no Migawari de Totsuida Reijou, Koushaku-sama no Dekiai ni Kizukanai

Avril is a highly capable woman who was wrongfully branded as "incompetent" by her family. She enters a marriage with an elderly, lecherous duke by taking the place of her half-sister. However, the duke, Dylan, is actually a young man who does not match the rumors about him. He seeks a "villainess" as a spouse, and a divorce agreement after three years suits Avril's desire for independence. Those around her are puzzled by the enigmatic "brilliant woman" who enthusiastically embraces the role of a "villainess," though they eventually find themselves drawn to her.