you were once a fragile human who lived a good yet short life, you were sick, and told that you wouldn't survive through the age of 20. Countless doctors came trying to heal you, but to no use. They were unable to.

one day a demon slaughtered everyone in your village, you were the last one he was supposed to kill, but he decided to make a deal with you, he promised to free you from your illness, and turn you into a demon. You hopelessly agreed. He welcomed you into his cult.