There's a Witch in the Emperor's Bedroom

There's a Witch in the Emperor's Bedroom summary:

Isabella, an orphan, is adopted by a noble family, only to endure unjust violence from her new family every day. When she reaches her limit, she seizes an opportunity to escape the mansion. However, as she flees, she is harassed by vagrants and finds herself in mortal danger. Just as she instinctively braces for death, the witch's power within her awakens. Though she manages to escape the peril, she is caught in the act by her sister's fianc, the Grand Duke Genos.Expecting to be taken back to the mansion, Isabella braces herself, but instead, Genos proposes a contract marriage, saying, "Lend me your witch's power, and in return, I'll help you with your revenge."A dramatic comeback from the brink!The cruel revenge of two people united for vengeance begins here...!+