I know this is a long shot, but I have to try.
I remember reading an ongoing story about a woman that stubbies into a BDSM relationship with a demon. Pretty standard so far, but the trust of the story was that she is a Fell, a being the literally burns the sin from existence by magnifying it. This is why she had an overall shitty life up to that point.
There is more I remember, but I also don’t want to spoil too much for anyone else because it was a really good series.
P.S. I think I originally read the story on Literotica, but I can’t be sure.
Source: reddit.com/r/Erotica/comments/tuzs4u/finding_an_old_story