Hakushaku to Yousei Noroi no Daiya ni Ai wo Komete

Much to her chagrin, fairy doctor Lydia has failed to convince her employer, Earl Ashenbert, to call off their engagement. As much as she tries to see through his flirtations, he still seems to have her wrapped around his little finger. The appearance of the moonstone’s steward, a small fairy called a coblynau, doesn’t help—it turns out he’s a strong supporter of their union! Meanwhile, Edgar comes into possession of a cursed black diamond that is said to bring its owner great misfortune. Just how does it tie into his revenge against the Prince? (Source: J-Novel Club)