Who is Luna Kaftan from On a Pale Horse and what is their importance?

Luna is the daughter of a black magician. She loves her father dearly and also respects him. This love and respect for her father overrides all of her other instincts, including self-preservation. Luna's sins are all for the sake of her father, allowing her to be both a soiled, fallen woman and a pure, virginal woman simultaneously. Unknown to her father, Luna learned black magic by summoning a demon and letting him rape her mind. She did this to help her father, and it has marked her soul with sin. Zane forgives Luna this sin because her desire to help her father, whatever the consequences to herself, resonates with his desire to help his mother.