Manga information: Nullitas: Itsuwari No Hanayome

Nullitas: Itsuwari No Hanayome summary:

Dreaming to be a knight, an unnamed girl who grew up as a boy. In fact, she was actually the illegitimate child of Count Romagnolo, who she worked under as a servant. Eventually, the Count found out her existence, and she was sent as a replacement bride for her blood-related sister that the Count endeared more. So she was given the name “Núllǐtas”, and let's see how her life changes onward.