She's from a modified Beauty&the Beast story, that includes more fantasy and horror elements. Lady Clarity comes into the story when the protagonist goes looking for information, and aid. She provides crucial information and clears up several points of confusion, and becomes a strong ally to her.

Lady Clarity is brave, daring, romantic, loyal, practical, and dependable. 

She is a former knight, current minor noble. Her father was a knight, who performed a great service for a noble family. In exchange, the noble family pledged that their daughter would marry Clarity. However, events conspired to make that impossible. Although Clarity also became a knight, she eventually gave that life up, when the noble family offered to adopt her as their new heir. They had lost their own heir, and they still owed Clarity a boon for the actions her father had undertaken; raising Clarity to noble status fixed both of those problems.