There were two reasons she wore a mask. One, because she was the vigilante of the underground, killing those who do wrong. Two, if people found out who she truly was, she would be hunted down. She thought her life would always stay the same, until one day the Survey Corps decide they want her to fight against the titans. She agrees to join them under one condition, she gets to keep her mask on at all times - no one could find out who she truly was. Warnings - Graphic Violence. Rape is insinuated/referenced. Strong Language.