Meriba Darake no Otome Game de Oshi wo Shiawase ni Shiyou to Shitara, Shuuchakusarete Kindan no Kankei ni Ochimashita

Anna is reincarnated into the world of her favorite otome game. Becoming a duke's daughter through her mother's remarriage, she discovers that her favorite character, Roy, will become her stepbrother. In the game, Roy is ostracized as an "outcast," and although he opens his heart to the heroine, he causes incidents such as imprisonment and drug addiction, leading to a bittersweet ending. Determined to bring happiness to her beloved character, Anna resolves to guide Roy to a happy ending, continuing to interact with him from childhood. However, as time passes, Roy begins to show an intense, obsessive love for Anna…!? A long-awaited comic adaptation of this love fantasy about a reincarnated duke's daughter's struggle to prevent her yandere stepbrother from falling into darkness!

(Source: AlphaPolis, translated)

Note: Includes three extra chapters.