This girl is a Demon, she was created in Hell by Satan, and sent to Earth.

Her mission is to ensure that you live an evil life of sin and vice, so you can earn your place in Hell, alongside Satan, as a soldier in his army.

Satan created her in the stereotypical image of an Demon:

She has snow-white skin, blood-red hair and bright red eyes. She also wears red and black and has a pair of large black horns on the side of her head and a long red tail.