Fukushuu no Jikan

Kotoha was born into an affluent family, never having known hardship. However, her life is turned upside-down when her half-sister Ageha enters the picture. Fooling everyone with her childish "innocence," Ageha wastes no time hijacking Kotoha's life. Unable to see Ageha's true colors, even Kotoha's father begins treating her coldly. And before long, Kotoha loses her friends, her fiance, and any sense of belonging. Having been deprived of all she's held dear, she begins plotting revenge against Ageha in hopes that someday, she can knock her down from her pedestal. Now, Kotoha is ready, and it's finally time for Ageha to get what's coming to her...! (Source: MangaPlaza)