Carol is an artificial being that was created specifically to save mankind. Unfortunately, in him youth he suffered greatly at the hands of the very humans he sought to save and lost sight of his mission. Only through the kindness of one human girl named Shiori was Carol able to find his focus and a reason to save the world; for Shiori's sake.
If it goes to Carol gender. Carol is a male, he is in the form of woman because in it he can regenerate faster.