Hakushaku to Yousei Megami ni Sasagu Chinkonka

Lord Edgar Ashenbert is more eager than ever to marry his fairy doctor, Lydia Carlton. Having developed a deeper understanding of him, Lydia has found herself unable to spurn him the way she did before. Meanwhile, London has been plagued by a series of gruesome murders that seem to be linked to Edgar’s mortal enemy: the Prince. For the sake of Lydia’s safety, the earl insists that she come to stay with him at his estate. And thus the two suddenly end up living under the same roof... (Source: J-Novel Club)