Tsunderu Moto-Akuyaku Reijou wa Do-S Ouji-sama kara Nigedashitai

Anna, an ordinary office lady, is suddenly reincarnated as Anneliese, the villainess in a popular 18-rated otome game. There, she meets Prince Reinhardt, her fiancé and Anna's favorite character. Unlike the haughty Anneliese of before, Anna's cute mannerisms and shy reactions arouse Reinhardt's sadistic nature, and every night she is subjected to all kinds of lovemaking play...?
(Source: Gentosha, translated)