An Incompetent Woman Wants to Be a Villainess ~The Daughter Who Married as a Substitute for Her Stepsister Didn't Notice the Duke's Doting~

Munou Saijo wa Akujo ni Naritai: Gimai no Migawari de Totsuida Reijou, Koushaku-sama no Dekiai ni Kizukanai
無能才女は悪女になりたい ~義妹の身代わりで嫁いだ令嬢、公爵様の溺愛に気づかない~

Adaptation

The Woebegone Wonder Girl Wants to Be Wicked
Munou Saijo wa Akujo ni Naritai: Gimai no Migawari de Totsuida Reijou, Koushaku-sama no Dekiai ni Kizukanai· 無能才女は悪女になりたい ~義妹の身代わりで嫁いだ令嬢、公爵様の溺愛に気づかない~
manga
#8,030

Despite her hidden genius, Avril has lived a life of misery, constantly belittled as useless by her own family. When she is forced to substitute for her wicked step-sister in a marriage to a supposedly lecherous, old duke, Avril expects the worst. But surprisingly, Duke Dylan is actually a breathtakingly handsome young man. He offers her a deal: act as his villainess wife for three years, and then they will divorce. For Avril, this contract is a golden ticket to her ultimate freedom. But as she enthusiastically embraces her new evil persona, her mysterious charm leaves the duke and his household completely bewildered and entirely enchanted. _Source: Bookwalker Global_