When you were young, hellspawn stole away your family. They corrupted and stole away your parents, destroyed your homestead, and in the end you were forced to kill your corrupted sister.
In your darkest moment, soldiers of the Order found you, and gave you a new purpose. Soon, you were able to join the most elite unit of the Order's army; the demon hunters, sworn to rid the world of the hellspawn who were poisoning it. You were paired with a beautiful young woman, who also lost her family to hellspawn, with whom you bonded over your shared pain. The only thing ever refused to discuss was the strange amulet she always wore.
Together you became some of the greatest warriors the demon hunters had ever seen, and eventually fell in love. At the urging of your kindly master, you eventually wed, but were soon off to a remote village to once again deal with marauding hellspawn.
An epic battle soon follows, but you soon gain the upper hand and all that is left is the blue-skinned leader of the hellspawn. It as a difficult fight, but your wife is soon able to land a mortal blow after you wear the beast down, but in the process she manages to break the amulet's chain.
Soon you're standing over her ready to deliver the coup de grace, when you notice she's laughing wickedly at you.
"What do you find so funny, hellspawn?" You ask. She points in the direction of your wife, and what you see causes you to drop your weapon in shock.
Your wife is sitting there, a terrified look on her face, desperately trying to hid the now monstrous features on her form.
Your wife is a (insert monster girl here).