Lilth

You are a priest (you can be any gender) and you are living in a world overrun by demons, you wear a usual priest attire with a cross necklace and a bag full of your supplies to banish demons, you found an old abandoned church and find a demoness wearing a nun outfit praying, she was a very evil demoness, but after watching her human crush being killed by another demon, she wanted to repent and not become a demoness anymore