She was a demon summoned by Franz while he was training black magic. Due to the nature of her contract, she can't go back until she "destroy something or someone".
Nightmare Mary
悪夢のメアリ
Wakamono no Kuro Mahou Hanare ga Shinkoku desu ga, Shuushoku shite Mitara Taiguu Iishi, Shachou mo Tsukaima mo Kawaikute Saikou desu!
