Mary is a Hyakkaou school student, a school where all the students are gambler. She is a very gifted player but often cheats. She pretends to be calm and friendly, but is actually very arrogant and thinks only of herself. She always has a smirk. She sees students with indebtedness as inferior beings, and has a few to serve her. She is disgusted with the student council, and especially with the council president, Kirari. She is friends with Jabami Yumeko, although she finds her weird and scary.