The Bride Of Oblivion

Roberia, despite being the eldest daughter of a wealthy house, is called a "demon" by her family and locked away in an underground prison. She is chosen to take the place of her younger sister in an arranged marriage, but on the way to her new home she gets into an accident and loses all her memories. She then meets a man who claims to be her fiancé, Cecil. Cecil's kind and reassures Roberia that there's no need for her to recall her memories, but he strangely keeps calling her "Lily"... The mystery of her imprisonment by her family still remains, as well as what kind of love Roberia will find...

(Source: MangaPlaza)