Mary Anne is a detective with the Starry Sky Police, tasked within the film's narrative with protecting valuable cosmic entities known as Star Drops from exploitation. She employs a specialized device, the Miracle StarLight, to detect and gather these entities.

Physically, she possesses a canine-like appearance. Her personality combines a strong sense of justice and dedication to duty with notable clumsiness and occasional overzealousness in her methods. A keen sense of smell aids her investigative work.

A significant part of her duties involves pursuing the phantom thief Blue Cat, later revealed as Yuni (Cure Cosmo), due to Yuni's past thefts of Star Drops. Mary Ann faces considerable difficulty apprehending her, creating recurring comedic frustration alongside her professional obligation. Her simultaneous fandom towards Blue Cat adds complexity to this pursuit, as she admires the thief while attempting her arrest.

During the events surrounding the specific Star Drop designated Yūma (UMA), Mary Ann participates in shielding it from multiple groups of space hunters seeking to capture it for profit. Her responsibilities in protecting Yūma directly intersect with the Pretty Cures' mission against these threats.

Following the resolution of the primary conflict involving Yūma and the space hunters, Mary Ann successfully arrests the various hunter groups that targeted the Star Drop.