Konyakusha ni Wasurerareta Watashi Ringoku no Koutaishi Denka to Gisou Konyaku suru Koto ni Narimashita (※Tadashi, Denka no Honmei wa Watashi Mitai desu!?)

Leafe, the eldest daughter of a duke, is the reincarnation of the dark magician Laurie. In her previous life, she was feared as an evil woman of unparalleled wickedness and lived a solitary life. In this life, she has avoided loneliness and has successfully lived a smooth life surrounded by her family and fiancé. However, her younger sister Aria stole her fiancé and kicked her out of the house, returning her to a life of solitude. In order to attend Aria's engagement party and fight back, Leafe asks Oliver, the crown prince of a neighboring country, to be her partner. She thought this would be a one-off, but for some reason Oliver has asked her to marry him!?

(Source: Kodansha, translated)