Koushakuka wa Gikei ga Tsugebaii ~Ponkotsu Reijou no Akujo Keikaku~

"For my dear stepbrother... starting today, I'll become a villainess!"

Adele, the daughter of a ducal family, has long harbored a quiet affection for her stoic stepbrother, Edward. But just before her debut into high society, she learns a shocking truth: for Edward to inherit the dukedom, he must marry her. That kind of engagement... it would be too cruel for him! Thus, Adele hatches a ridiculous but heartfelt scheme...

Villainess Plan:
1. Become a selfish, scandalous villainess
2. Get herself disowned from the family
3. Break off the engagement so Edward can become the next Duke!

As Adele, a naive and clumsy young lady, struggles to "act villainous" out of love for her brother-in-law, she somehow finds herself in a love triangle with the crown prince...!?