"Once you tread on the path of darkness, you will tread on it forever. For the sake of the Abbey, I shall tread gleefully."
Blessed with looks and intelligence, Mary was loved by everyone in the town she was born, until her town was attacked by a vampire. They managed to take care of it, but not before the vampire, being drawn to her beauty, had bitten her. To her horror, the townsfolk turned on her next and she was forced to flee for her life.
A beautiful young girl by herself, a vampire no less, is bound to suffer greatly, but she managed to survive, defend herself, and when she could, she paid any grievances back with murder. Her life took a turn, however, when she stumbled upon Wisteria Abbey.
Mary entered seeking sanctuary, not knowing that the Church had simple ways to detect the undead. Yet, she had the extraordinary fortune that the sister on duty did not care. The kindness she was shown on that day returned her to the light. The sister and the abbess herself even allowed Mary to feed on them, and simply applied medicines produced by the Abbey to prevent infection.
From then on, she devoted herself wholeheartedly to the Abbey, such that she was able to inspire her peers with her diligence. A few years after she arrived, an epidemic hit southern Acadoria where Wisteria Abbey was located. The nuns of the Abbey did their best to treat the sick and dying, but many succumbed to the illness themselves. Mary alone was able to treat the diseased without fear. With her knowledge of medicine, her natural genius, she was able to find a cure through trial and error, and promptly visited the villages around the area saving thousands of lives. It was during these turbulent times that people began to think of her as some sort of saint.
Mary was not to be concerned by that, because when she returned to the Abbey, Mary realized that the sister who saved her had contracted the disease a while ago and was beyond saving, as she had gotten pneumonia and various other conditions as well. To incense her further, at the same time, another small monastery had figured out that Mary was a vampire when she went about treating people. They were blackmailing the Abbey to try to take credit for the cure. The cold anger and cunning from Mary's days as a lone vampire resurfaced. It was here when Mary discovered the power of the mob, and roused the people to attack the monastery without directly asking them. In the chaos, she slipped in and personally made sure the ringleaders of the incident were killed.
Mary acted contrite that her words had incited a massacre, but what she had truly felt was satisfaction, incredible satisfaction that the enemies of her beloved Abbey were disposed of. It allowed her to vent her grief that the person she loved most had died.
She continued to study medicine so that no one important to her would die of illness again, but she also continued to foster her reputation and standing. The rumour was spread that the gods had gifted her with immortality. When the old abbess died, Mary was unanimously voted to take her place. To this day, Mary continues to work tirelessly for the sake of her Abbey.