At first, Mary is shown to be incredibly sadistic and twisted. One example of her personality is how she treats her classmate Ryota Suzui after he turned into a "housepet" due to his low social status within the academy. She is shown cruelly taunting her opponents during their gambling matches. She's also shown to be extremely egotistical both in and out of matches, often being confident in her victory. Mary also possesses a habit of mocking her opponents and laughing at them, especially when match seems to be her win. She is a friend of Yumeko Jabami and a secret member of the criminal organization who pays hitmen contracts within the school and pays criminals to murder targets in exchange of money along with Kirari Momobami.