Itsuki uses cards manufactured by her father's company, which feature tiny heat-sensitive patterns or "marks" on the back that only she can identify. This allows her to "see" the cards before they are flipped. Yumeko’s "Madness" Unleashed
Following her loss to Yumeko in the premiere, Mary is seen struggling with her new status as a "housepet" (a student in debt to the council), enduring humiliation from her peers.
True to her nature as a compulsive gambler, Yumeko quickly realizes Itsuki is cheating. Instead of being deterred, she becomes ecstatic at the thrill of a rigged game.
