I wonder who ran this cult back on Isonatra and propped her up as a figurehead, back in the day. Looks like they had a whole theocracy going over there, which takes a level of organisation that I don't think would have been achieved by just fanatics like this person, and Lin really does not seem to be the type to come up with anything of this sort either, so I assume there to be someone pulling the strings from the shadows.
If a person like that exists, they presumably would have been the one who kept Lin performing her role as the "Saintess" by guilt-tripping her about how much worse things could be if she did not keep up her end of the facade (and by extension, also the one to condemn Rachel when it became clear that her existence made Lin waver in her convictions).
So if I am at all correct about any of this, I would not be surprised if that were the final antagonist of this comic.
It would depend on whether the cult is part of the aggressive, expansionist empire that Lin "sacrificed" herself to (and then inadvertently became the mana-battery for Rachel), or if it originated in her own kingdom that she first became the saintess in, where she helped people with her power to heal.
If it's the former....then yeah, definitely terrifying, but also I don't recall there being much in the way of Lin being "the saintess" while captive, as she was effectively tied to Rachel the whole time, up until the Empire's collapse and Rachel was put to death in the ensuing fallout.
If it's the latter...I'm wondering if maybe they started out "legitimate", but when Lin sacrificed herself and fell into that Empire's hands, they went apeshit without their saintess, and fell into fanaticism and took to extreme measures.
In any case--quite wild that so many people seem to have crossed over. Which makes me think that if there is some shadowy leader behind this cult group (and I very much agree that they must exist, and are likely some endgame antagonist), then they must be very powerful,
and have laid lots of groundwork and plans to follow Lin into this life/world en masse with many others to try and continue whatever dominion plan they were hatching before. And saying that...I kinda suspect that this group is from Lin's original country, rather than the Empire--they would have enjoyed the luxuries that came with following a saintess who went around being benevolent, and then lost that privilege when she was taken away. They probably are even behind Rachel's initial death, if I'm correct thus far.
Which would all be kind of neat as a twist, in that it wouldn't even be "Lin's Original Enemy" coming after her, but some twisted & corrupt iteration of her own people.