Magic comes in two varieties, "white" and "black". Despite what they are called, the names of the magic types do not necessarily associate with any kind of "moral alignment". Black magic could be used for good just as easily as white magic could be used for evil. However, most demons prefer black magic, and those who fight them tend to prefer white magic. The primary difference between them is where the magic's power is drawn from. Black magic is drawn from the emotions and feelings of the body, while white magic comes from the thoughts of the mind.
Black Magic: The power of black magic is drawn from emotion and feeling, and thus is most easily able to affect the bodies of others. Demons and monsters often use black magic in order to aid in the rape and corruption of innocents, as arousing a target is one of the first things a disciple of black magic learns. Black magic can also change the size and functions of bodily parts in strange ways, but it is incredibly difficult to use on oneself, as it interrupts the flow of power from the body. Most users of dark magic only learn to draw their power through their lust, rendering it impossible to use when turned off.
White Magic: The power of white magic is drawn from the mind, but is more often called the power of the soul. White magic is considered "stronger" than black magic because it can be used to create energy from nothing or heal the body. Users of white magic can blind their opponent with dazzling lights, burn them with pure white flames, or even magnetically charge weapons and armor to repel each other, making them more resistant to attacks. White magic requires significant mental discipline and awareness, and becomes impossible to cast if the user is greatly distressed or aroused.