Dokushin Shugi no Reijou wa, Koushaku-sama no Dekiai kara Nogaretai

Elentina, the daughter of an Earl, has decided to remain single for the rest of her life, hiding the fact that she is a "witch." Just when she was finally able to break off her engagement with the man her father had chosen for her, Duke Arden has somehow proposed to her!? I don't want to get married while keeping my true identity a secret...so I'll have to break off our engagement again! She decides to do this and tries all sorts of schemes, but the Duke won't give up at all! (Source: Kadokawa, translated)