Hanayome to Akuma no Yakusoku

Marie, a naive girl living a humble life as the daughter of a country nobleman, assisting the peasants, is offered a marriage by her parents-in-law. Her stepfather offers her a marriage proposal, but it is to the "Lord of the Devils," a man who is the subject of many frightening rumors. Marie's relationship with her step-parents is not good, but she is indebted to them for raising her, so she decides to accept the marriage proposal. However, when she visits the Devil Lord's mansion, she finds an unexpected truth awaiting her.

(Source: Comic Days, translated)