Mary Saotome attends Hyakkaou Private Academy as a second-year scholarship student, transferring from an ordinary, financially limited family. She possesses average height, long blonde hair usually styled in pigtails secured by black ribbons, and dark yellow eyes. Her attire is the standard Hyakkaou uniform: a red blazer with black trim and gold buttons, a white button-up shirt, black tie, gray pleated skirt, black socks, and brown loafers. Adapting to the academy's gambling hierarchy during her first year (*Kakegurui Twin*), Mary focused on social climbing through calculated risks and strategic cheating, using her intelligence to exploit opponents. Key events involved winning a gambling den from Yukimi Togakushi and forming alliances, notably with childhood friend Tsuzura Hanatemari. Witnessing Tsuzura's mistreatment as a housepet fueled Mary's hatred for the system. While pragmatic in leveraging alliances for personal gain, this period revealed her capacity for loyalty and protective instincts towards Tsuzura. A significant personality shift followed a high-stakes loss to Yumeko Jabami in the main series and Mary's subsequent demotion to housepet status. This defeat and humiliation shattered her initial arrogance, sadism, and egotism—previously exemplified by her cruel treatment of housepets like Ryota Suzui—eroding her pride and leading to a more tempered demeanor. Though still easily provoked by recklessness or cowardice, she gradually developed genuine bonds with Yumeko and Ryota, shifting from pure self-interest to collaborative efforts. She teamed with Yumeko in the Debt Settlement game to overturn their debts. Mary's gambling style relies on probability calculation, psychological manipulation, and opportunistic cheating; she frequently loses initial rounds before adapting to opponents' tactics. Driven by resilience and a determination to reclaim her status, she challenges the student council's authority, particularly President Kirari Momobami, whom she blames for the housepet system. This evolves into political ambition in *Kakegurui XX*; after aiding Ryota and Yumeko in the election arc, she declares her intent to become student council president. A lingering trauma stems from Tsuzura's unexplained absence in the main series, hinted at through Mary's preservation of a hairpin from her and her intensified grudge against the council. Her family's emphasis on achieving victory as a "true winner" remains a core motivator, amplifying her disdain for those who underestimate her due to her socioeconomic background.