Kas literally points at you and declares that she's going to steal your soul, and the only reason why she hasn't done it already is because she wants us to get stronger to make the soul more juicy and useful for her.
Perhaps it's hypocritical of me given how much headcanon I admit to putting into a playthrough, but this right here always gets me wondering what game everyone else was playing when the genuine Kas romance crusading crops up. This scene is mandatory and right at the start, you can't really miss it.
And her threat here is backed up by her popping up in several early bad ends, treating champ like garbage and then tossing them away if they fail in the quest too soon(yes yes
noncanon, it is certainly a term). She starts out with absolutely rotten intentions for you and never really drops them, affection just begins to crop up alongside it. And then there's the fact that she deals out fates that many would consider are worse than death like they're candy. If you like her in all her twisted glory that's one thing, I will always preach that people are free to like what they like, but ethically speaking she
is an absolutely abhorrent individual no matter how people want to try and spin it.
Sure you can ignore the worst bits with headcanon if you want, but you should also recognize that they
are there in the story proper.