Renner Theiere Chardelon Ryle Vaiself serves as the Third Princess of the Re-Estize Kingdom, youngest daughter of King Ramposa III and half-sister to Crown Prince Barbro and Second Prince Zanac. Celebrated publicly as the "Golden Princess" for her perceived benevolence and wisdom, she earned this title through instrumental reforms including the abolition of slavery and advocacy for policies benefiting the poor and orphans. Her appearance reinforces this image: long golden hair, sapphire-blue eyes, and attire emphasizing purity, typically a fashionable white dress accented by a golden necklace.

Beneath this façade, Renner exhibits a psychopathic and manipulative personality. She lacks empathy, viewing most humans as tools or obstacles, and commits morally reprehensible acts without remorse. Her exceptional intellect enables her to deduce complex schemes from minimal information, such as uncovering noble betrayals through maid gossip. This detachment originated in childhood isolation; her advanced cognitive abilities alienated others, preventing meaningful connections until encountering Climb, a street orphan she took in as her personal bodyguard. Climb represents Renner's sole emotional attachment, though her love manifests as a possessive obsession. She explicitly describes wanting to "chain him up completely and raise him like a dog," valuing him as her most cherished "pet" or "puppy." This fixation drives her actions, including deliberately endangering him during missions to create scenarios forcing complete dependence, such as orchestrating situations where his potential death and resurrection would leave him physically weakened.

Renner's loyalty to the Re-Estize Kingdom is superficial. She secretly collaborates with Nazarick, particularly Demiurge, after he recognizes her intelligence and malice. Their alliance targets the criminal syndicate Eight Fingers, serving both Nazarick's interests and Renner's ambition to elevate her public image. During the demonic disturbance led by Jaldabaoth (Demiurge's alias), she strategically deploys adventurers and royal guards, accepting casualties as expendable. She ultimately betrays her kingdom in exchange for Nazarick's promise of eternal union with Climb and a racial transformation.

Following this betrayal, Renner undergoes a race change into an imp demon, altering her appearance: her hair lengthens, eyes darken, fangs and claws emerge, and small wings develop. She adopts black attire, including a dress and heels, replacing her crown with a black rose. This transformation eliminates her need to conceal her true nature, except around Climb. Her treachery culminates in assassinating her father, King Ramposa III, stabbing him in the back with the royal sword Razor Edge during the Sorcerer Kingdom's invasion. This act solidifies her allegiance to Nazarick, where she becomes known as the "Witch of the Falling Kingdom."

Renner operates with cold pragmatism, aligning with Nazarick due to their capacity to fulfill her desires. She acknowledges Ainz Ooal Gown's authority, fearing his power while respecting his leadership. Albedo, noting Renner's heteromorphic mentality despite her human origins, considers her a kindred spirit in depravity but threatens Climb's life should Renner ever betray Nazarick. Within Nazarick, Renner abandons her princess persona entirely, though she maintains her unrestrained devotion to Climb, liberated from her former human morality.