Brunhilde is the eldest of the thirteen Valkyrie sisters and serves as the primary strategist for humanity in the tournament of Ragnarok. She is a striking figure with long, midnight blue hair, pale skin, and piercing emerald-green eyes, typically dressed in a formal white gown with gold and navy detailing. Her background is unique among the divine as she once fell from her status as a full goddess to a human level, becoming a demigod. This experience of living among mortals forged a deep and genuine bond with humanity, giving her a perspective that most other gods lack and providing a powerful motivation for her actions.

Her personality is a complex duality of cold calculation and deep, hidden compassion. In public, especially before the gods, she presents herself as brave, intelligent, and serenely confident, often displaying an arrogant and provocative demeanor to goad her divine opponents. She is a master strategist, capable of making ruthless decisions, such as sacrificing her own sisters who perish when their human partners are defeated, and even coercing one sister, Hlökk, into a forced Völundr with the serial killer Jack the Ripper to secure a tactical advantage. However, this icy exterior is a shield for a profoundly empathetic soul. In private, she bears the immense weight of her choices, grieving intensely for the fallen Valkyries and human fighters at a personal shrine. Her stress manifests in a notably human and almost comedic way: she binge-eats large quantities of salmiakki pie, a bitter and acquired taste, whenever she is overwhelmed.

Brunhilde’s primary motivation is the salvation of humanity from unanimous divine decree of extinction. She single-handedly proposes the Ragnarok tournament as a last chance for mortals, taunting the gods into accepting by questioning their courage. While her surface goal is humanity's survival, deeper layers of motivation are implied. Her imprisonment of her boyfriend, the demigod Siegfried, in the depths of Tartarus is a significant catalyst for her actions, suggesting that Ragnarok is also a means to a more personal end. Her past, including the exact circumstances of her fall from grace and return to divinity, remains shrouded in mystery, hinting at further hidden agendas.

In the story, Brunhilde acts as the narrator, the commander of the human effort, and the soul of the conflict. She is responsible for selecting the thirteen human champions from across history, known as the Einherjar, and matching them strategically against specific gods to exploit weaknesses. She also orchestrates the Völundr, a divine ability where a Valkyrie shares her fate with a human fighter and transforms into a divine weapon capable of harming a god. Her key relationships are central to her character. Her bond with her youngest sister, Göll, is an iconic duo act; while Brunhilde often chastises Göll for her naivety and shows her a cold, pragmatic face, she deeply loves her and all her sisters, even if she does not openly display it. Among the gods, she shares a complex history with Heracles, a former friend whose death in the tournament she mourns privately. She also has a history with Buddha, who taught her the secrets of Völundr, though she finds him to be a terrifying and unpredictable ally. Her relationship with the human fighters is purely strategic; she feels personal disdain for figures like Jack the Ripper but will use anyone necessary to secure a victory for humanity.

Brunhilde’s development throughout the series is a gradual fracturing of her stoic facade. Initially presented as unflappable, the consecutive deaths of her sisters and beloved human champions like Adam and Raiden cause her visible despair. However, she channels this pain into a fiercer resolve, her rage and sorrow fueling her determination to win at all costs. She has privately confessed that she plans to subject herself to eternal oblivion in Niflhel as an act of atonement once Ragnarok is over, revealing the immense guilt she carries for leading her family and allies to their doom. While her direct combat abilities remain largely undisclosed, her true power lies in her exceptional intellect, her knowledge of divine and historical figures, and her mastery of strategy. She is the architect of humanity's survival, and her own destiny remains one of the central enigmas of the conflict. Note that the query specifies Record of Ragnarok III; however, the available information pertains to the main Record of Ragnarok series, in which Brunhilde is a central figure from the outset.