Nullitas ~The Counterfeit Bride~

One day, a girl who was raised as a boy has her entire life flipped upside down...

A nameless boy who dreams of becoming a knight works as a servant for the renowned Romagnolo family. One day when he is seventeen years old, the boy faces his first monthly period and his mother tells him that actually, he is a girl. She is Count Romagnolo's illegitimate child and her mother secretly raised her as a boy to protect her.

When the count finds out about his illegitimate child, he decides to use her as a pawn to protect his daughter, Maylene, from an unfavorable engagement. In that instant, the child who has lived for seventeen years without a name is given one, and her life begins to change dramatically. Her name is "Nullitas," which means "nothing."

(Source: Pocket Comics)