Akuyaku Reijou nanode Last Boss wo Kattemimashita

Aileen Lauren Dautriche's engagement to Crown Prince Cedric is publicly broken, and in the middle of the humiliation memories from her previous life return. She realizes she has been reincarnated inside an otome game as its villainess, complete with knowledge of the ending waiting for her: within months, she is destined to die at the hands of Claude, Cedric's half-brother and the story's “final boss,” the Demon King. Instead of waiting, Aileen decides to break the script and asks the most dangerous man in it to marry her. Claude distrusts her, so she begins proving herself by helping protect demonic beasts and pursue peace with humans. The further she moves away from the original story, the more she discovers that the game contained more than one bad ending.