So, not the cult of fanf AU (name in work), but I had another AU idea:
Long ago, before the world's split, there was a god. The god was loved by all, their temple a home for any who needed. Many of their Paladins and clerics choose to be bound by the oath of marriage and take on any. The temple was always full of the disabled, the young, and those who wish to care for others. Each movement in their temple gave them power despite never once fighting they were among the strongest.
But one day, the world spit, war raged, and the people realized that despite their power, they could not fight. One by one, those who stayed left. And the once beloved god was quickly forgotten.
Now, all that's left is a ruin far in the woods, the once great temple now part of the forest. It's said that the god still resides there, no longer a god, but not mortal. Their cries echo from far in the trees, morning those who they loved and the betrayal of those who said they love them.
Now, two adventures lost in the forest hear their cries. Not knowing the stories of these lands wander to assist, and suddenly, somewhere, the page of a storybook flips.