The character known as Aunt is officially named Aunt Marie within the extended family of Mario and Luigi. She appears as a member of the brothers' close-knit Italian immigrant family, all of whom live together in the same building in Brooklyn. Her background is that of a paternal aunt, and she is presumed to be the wife of Uncle Arthur, another family member who appears in the film.

In terms of personality, Aunt Marie is presented as a straightforward and observant relative. While her screen time is very limited, she displays a no-nonsense attitude, particularly in her interactions with her husband, Uncle Arthur. Her primary role in the story is not to advance the main plot of Mario and Luigi's journey to the Mushroom Kingdom, but rather to establish the brothers' ordinary life and strong family ties in Brooklyn before their adventure begins. She is part of the family dinner scene that helps ground the characters, showing their working-class roots and the familial support system they come from.

Key relationships include her connection to Mario and Luigi, whom she greets upon their arrival. Her most notable dynamic is with her husband, Uncle Arthur. In a brief moment, she is shown scolding him, saying Hey! which demonstrates a familiar, slightly corrective but ultimately affectionate dynamic between the couple. This interaction adds a layer of authentic, everyday family life to the film.

The character does not undergo any development, as she is a minor background figure with no arc of her own. Her primary function is to populate the world and reinforce the theme of family. Her most notable ability, within the context of her limited role, is her commanding presence within the household; a single word from her is enough to get her husband's attention and correct his behavior, showcasing her as a quietly authoritative figure at the family dinner table.