Nina the Starry Bride

Nina is an orphan who lives in the slums with Korin and Saji, two orphan brothers like her. She hides her identity as a girl and bears the name Ninaf to avoid being sold as a slave because of the rare color of her eyes. She goes to steal for Korin who is sick and ends up being sold. She is bought to become a substitute for a conveniently dead princess who had the same eye color. In three months, she will have to learn the manners of a noble and will be married off to a prince from another country.