Madeline is a demon. She was once human, but made a bond with four demons to exact revenge on those that tormented her during her human life. The way she worded her contract was accidentally never-ending, so she and the demons can never separate or die. She continues to exist, taking souls of people she passes to feed her demons.
She has many different forms with no definite shape. The only details consistent is that she is always female and colored black and white with her tattoos.
Her personality is mostly monotonous, and she mostly prefers being alone. There are few who have interested her, and even less that she is willing to converse with.