She is the character with the most common sense in the series, and is the only one who understands the problem between Hayate and Nagi. She appears to be the one in charge of everything in Nagi's manor, since everyone from the head butler to the SP either obeys or fears her (or both in some cases). She's good at general housework and likes games of all kinds, though she is scared of "the dark life-form that exists in the kitchen and other places". She also proved capable of self-defense techniques in times of need.
She has no last name because she was an orphan who was found next to the statue of St. Mary at a church, which is where she got her name. Not knowing anything about herself, her birthday was decided as December 24, the day she was found. She is the unfortunate one who always has to clean up everyone's messes. She has seen Hayate naked several times, and she sees the effect he has on other girls, many of whom are attracted to him for his kind nature although she has trouble determining if she herself is one of them due to her lack of first-hand experience with interpersonal attractions. Maria is also legendary throughout the school for having graduated high school at the age of thirteen in just three years while maintaining the position of Student Council President for two years.