Marleeri's parents are relatively normal, and live in a small town in Barstoi, Ustalav. Her father is a hedge wizard who makes a living off of crafting and selling minor magic items, mostly potions and scrolls. He specializes in a special brew he claims is superior to any healing potion, that regenerates your wounds before your very eyes. Marleeri's mother is an enigmatic adventurer. She's in and out of town frequently, but spends almost every moment in town with her husband. She's renowned as a great warrior, though nobody in town claims to have ever seen her fight, and rumors suggest she has magical powers and might have even slain a dragon.
Then Marleeri is born... and little changes. She's a beautiful, human, baby girl. Her parents were stressed before the birth, but are relieved. They live happily for a few years, with Marleeri's mother settling down. She still occasionally leaves for business. Marleeri's father tries to teach her magic, but she has no aptitude for it. She grows incredibly slowly.
On her 6th birthday, disaster strikes. Scales grow from Marleeri's flesh around her hands and feet, a sinuous tail extends from her spine, and a small pair of horns erupts from her brow- she is clearly a tiefling, though her demonic nature has manifested late. Her mother is out of town, and the superstitious villagers are horrified. Marleeri is sequestered away, and her father is taken by a mob, tried for dallying with demons, and promptly executed. Marleeri is left imprisoned while they decide what to do with the abyssal child. Her mother returns, and learns about what happened in her absence. In a rage she abandons her disguise and reveals herself to be a succubus. She reclaims her child, and in the process leaves a large portion of the town in flames.
But Marleeri's mother is afraid now. Her child has been damaged, her innocence tainted by the murder of her father and the sight of her mother killing and destroying. She doesn't think she can be a good mother alone, so she leaves Marleeri with the only people she can trust to teach her daughter properly, and hopefully not to hate her for what she had done, but to understand her; the heretical cult of Nocticula.
Now she's made her way to Kenabres, with intent to join the crusaders and battle against the Worldwound.