Mary was the late wife of Viktor Fleischer, serving as the true antagonist and final boss of Rise of Nightmares. Mary was born in the aristocratic Thomas family, she was eventually married to Viktor and had a child together.

Her husband's obsession with superhuman studies soon got the better of him and he performed a surgery on their child in order to make him "perfect", however their child did not survive the surgery. Stricken by grief after the death of their child, Mary blamed Viktor and held him responsible. Viktor became enraged and strangled her to death. Viktor regrets for what he had done and swore that he will bring her back by perfecting the dark arts of raising the dead. Viktor repressed his awareness of Mary's death, which eventually led him into cross-dressing as her to believe that she was still alive. Her husband soon discovers a mansion located deep in the forest of Romania containing a treasure trove of historical documents and ancient alchemic tools that could help advance his research. Viktor was able to brought back Mary's ghost, now transformed into a malevolent being, by constructing a large statue in her likeness on an altar in the forest. Viktor continuously practiced experimenting on O Zhuvindo (life force) he extracted from the victims of his demented research, hoping o one day find the life force suited for Mary.