Mary Saotome is a second-year scholarship student at Hyakkaou Private Academy, hailing from a non-wealthy family. Her ambition fuels a drive to climb the school's gambling hierarchy. She possesses long blonde hair styled in twin pigtails secured with black ribbons, dark-yellow eyes, and wears the standard Hyakkaou uniform: a red blazer with black trim, white button-up shirt, black tie, gray pleated skirt, and brown loafers. In the prequel spin-off *Kakegurui Twin*, Mary arrives as a transfer student displaying a significantly milder personality than her main series introduction. During this period, she forms key friendships with Tsuzura Hanatemari and Yukimi Togakushi. While employing calculated gambling strategies, she avoids intentionally ruining opponents and demonstrates concern for others' well-being. This time reveals her strong sense of justice and empathy, particularly in protecting classmates, though these traits become suppressed following unresolved events involving her friends' departure. Mary keeps a hairpin from Tsuzura as a memento, indicating lingering emotional attachment. At the start of the main series, Mary's personality shifts toward arrogance, sadism, and overt competitiveness. She cruelly dominates housepets, exemplified by her treatment of Ryota Suzui after he incurs a 5 million yen debt to her, using him as a footstool and servant. Her position collapses when Yumeko Jabami transfers in; Mary attempts to manipulate a rigged Vote Rock-Paper-Scissors game to turn Yumeko into a housepet but loses after Yumeko exposes her cheating. This defeat reduces Mary to housepet status, enduring bullying and desk vandalism. Desperate to regain status, Mary gambles against Student Council member Yuriko Nishinotouin but suffers another loss, accumulating nearly 5 million yen in debt. She receives a life plan from the Student Council dictating her future marriage to a politician, intensifying her resentment. Forced into the Debt Settlement Gathering, she partners with Yumeko in Two-Card Indian Poker. Their coordinated gamble defeats Jun Kiwatari, clearing Mary's debt and restoring her status. This collaboration marks a turning point, as Mary gradually develops a complex alliance with Yumeko and demonstrates concern for her well-being, though remaining critical of Yumeko's recklessness. Following reinstatement, Mary's arrogance diminishes, replaced by fierce opposition to the housepet system and the Student Council's manipulation of indebted students. She declines President Kirari Momobami's invitation to join the Council, openly criticizing their dehumanization of housepets despite Kirari pointing out Mary's prior participation. During the student council election arc, Mary intervenes in high-stakes gambles to protect Yumeko, deducing card-shuffling patterns to outmaneuver opponents in the Nym Type Zero game. Her strategic acumen secures victories, and she expresses ambitions to become student council president. Mary's gambling abilities emphasize analytical precision over Yumeko's risk-taking. She excels at detecting cheats, formulating counter-strategies, and exploiting game mechanics, such as identifying shuffling patterns or orchestrating multi-layered bluffs. Her skills develop through numerous gambles in both the main series and *Twin*, showcasing adaptability and tactical foresight. Her relationships evolve significantly: initial disdain for Ryota Suzui softens into mutual respect and subtle romantic tension, while her antagonism toward Yumeko transforms into a complex alliance rooted in shared defiance of the academy's power structure. Her interactions with Student Council members remain adversarial, particularly toward Kirari and Vice-President Ririka, whom she prods to act independently. Key personal details include her birthday on March 8 (Pisces zodiac sign), height of 162 cm, and preference for romantic partners characterized by absolute honesty. Her speech style shifts from polite formality with superiors to blunt or crude language with peers and enemies.