When I Was Reincarnated in Another World, I Became the Stepbrother of a Villainess Who Faced Ruin Not Matter What

My name is Robert Vincent. I am the legitimate heir to a family of dukes. I have a stepsister who is like an angel. Her name is Cecilia Vincent. She appears as a villainess in the popular otome game Sekai wa Kimi wo Kuni wo Yorimete, or ‘Sekakoba’ for short, which was popular in my previous life. As a villainess she meet bad endings in all the routes… By the way, if my stepsister meet the bad end , the whole family will fall as well . Is the entire family cursed? For now, my goal in this life is to make ‘Cecilia’, who is the cause of the downfall of the entire Duke Vincent’s family, follow the straight route to a ‘happy ending’