Huh, seems like the little sister is living well even though she caused the entire city to...

I think the prophesy is a hoax, I think her mother put the book for her daughter to read and believe so that they can point it to the real avier for sacrifice to make that vech to look tragic damsel, then the prophesy becomes real because Nive got angry in the cave, remember her emotions can reflect her surroundings for example Nix's office got rained, the her anger towards the human on that place got wiped out hahaha

I think you need to read it again. The prophecy was always fake, the sister hired dudes to kidnap the MC when she went in the cave because she was jealous the MC and ML got along so well. The spirits then got mad and destroyed everything because they were being used as an excuse for evil deeds. They never needed a sacrifice or anything.

But what I'm saying is that it seems like the sister and mother probably made up some lie about the MC angering the spirits when she went to sacrifice herself (or maybe they made a lie about her running away) and that's why everything got destroyed. Remember when MC exits the cave, th merchant guy tells her not to use her surname around here, probably because her or her family was blamed for the destruction. But it seems like her sister is still living well, so they managed to push all the blame on the MC, not the family.

Σ( ￣□￣||) oh my gad, I can't wait for the reveal