An Observation Log of My Fiancée Who Calls Herself a Villainess (2018)

Blurb:
Because Prince Cecil is extraordinarily intelligent, life is boring for him. His days are without much excitement, but he becomes engaged to Bertia, the daughter of a marquis. The first thing she says to him when they first meet is quite baffling. She claims she is the “villainous heroine” in the story of his life!! According to Bertia, she has memories of her previous life. In a certain “romance game” she played in her life before, she played the character of the “villainess.” Her purpose in her new life is to become an exemplary villainess and ruin the prince’s engagement. In order to achieve this goal, Bertia does one outrageous thing after another and brings chaos and confusion into his life. A unique “love” story with a twist!!

Source: www.anisearch.com/manga/43750