Mary is a necromancer, the only one in the world. Mary was a child when she nearly died due to the amount of dead mana she absorb during an incident in her childhood which left her an orphan. Ovante and Tasha found her and took take of her. In order for Mary to survive, she could either become a black mage or a necromancer. However, this meams that she couldn't walk around freely since humans and other races hates species with the darkness attribute, especially the people from the Church of the Sun G** whose G** used to fought a powerful necromancer back then (the one Cale was mentioning previously).