Hakushaku to Yousei Propose wa Oteyawaraka ni

Fairy doctor Lydia has been hired by Edgar, a smooth-talking earl with a tattered past. Her ability to see and talk to fairies proves invaluable when his London estate is visited by a tiny fairy of the field. The fairy has come to fetch the Blue Knight Earl—Edgar—to marry the Fairy Queen. Unfortunately, the moon-embedded ring to complete the proposal has been stolen! Not only that, but Lydia has to deal with the reappearance of a wild kelpie from her hometown—one who also has his sights set on marriage... (Source: J-Novel Club)