Jishou Akuyaku Reijou na Konyakusha no Kansatsu Kiroku

Crown prince Cecil was so brilliant that everything in life was easy to the point of boring him, then one day, his fiancée Bertia suddenly said "Prince Cecil, I am a villainess!" Claiming that this world is the same as that of an "otome game" from her past life and that she is playing the role of the "villainess" in it, she aims to play her part well and have their engagement annulled. With that goal in mind, she sets about causing turmoil in Cecil's daily life.

(Source: MangaDex)