Mary Sue or Mary Sioux is one of the main antagonists of the series. She is the sole daughter of Anson Sue and his wife, who hailed from the Unified States. She fled her homeland of the Legadonia Alliance prior to its fall to the Empire to the Unified States alongside her mother. Following her father's death at the hands of Tanya von Degurechaff, she enlists in the nation's armed forces as a volunteer to seek revenge and becomes a member of the Multinational Mage Unit.