I wonder what happen if the saint they summon/kidnap resent them instead of helping solve ...

I don't think a person who would take that route would ever become the Saint. Maybe they could turn against them later if the people did something more horrible that causes them to be 'corrupted' so to say. I do think that the person would have to have a certain disposition to end up becoming the Saint, so it would be really interesting to see that happen.
I've seen it with summoned heroes, but I can't remember any stories where it's the Saint that turns on them.

What if that someone is like kondou who happen to tag alone with the saint, but he/she able to adapt to that world and use magic too unlike kondou who don't have divine protection. And take revenge on them.

I feel like people take the saint for granted and expect her to stay with them forever even after the mission is over. Did they properly ask the saint what she want.They kinda kidnap her from her world just to solve their world problem. They rely on the saint completely to solve the miasma problem.

The tag along is definitely more fair game. Though you still need to consider that their god may have wanted Kondou here to do exactly what he is doing now. Helping their world grow and progress. Though this may not be the case with other situations, and there could be room for error in the summoning.

I think I have a story where the tag along that got summoned with the desired target gets revenge on them, though its provoked and not just because they were summoned. Let me look through my stuff. I've also got heroes turning their backs on the people who summoned them, but I'd have to poke around for a Saint.

Your other point would count on the doing something horrible to break/corrupt the Saint category. Kidnapping someone and putting all the responsibilities of the world on them and when they are finally finished, they are expected to stay with these people who only care for them because of their position forever. Even if they are very adaptable, that would slowly ware on someone, and we can already see it happening to our Saint here. But now what we need is a betrayal of expectations. I can't see our Saint or any Saint turning against them just from this. The most I can see happening is them just leaving and going to live their life somewhere else.

Now, if they dangled promises of returning home in their face to get them to fulfill their purpose only for the Saint to find out that they were lying the whole time. Now that could be dangerous. Or if they lied to the Saint about the actual dangers they would be facing (such as going up against demonic forces) and they just have them murdering a race that wants peace. (I've got a similar story) There's a lot you can do to break your Saint, but you'd want this outcome to feel realistic instead of just a forced plot outcome for the writers desired story.

In the case of our Saint here, if she were to just turn on them and abandon her responsibilities, what do you think would happen? She'd have an entire country after her and if they do catch her she'd receive far worse treatment. They'd probably forcefully bring her along on expeditions and make her purify the miasma wile threatening harm. And they just might kill her or lock her up in a dungeon somewhere when they don't need her anymore. She has no way of protect herself without the help of others since her abilities are not capable of harming people. She would need to collect people to protect her, but who in their right mind would do that in this situation where their country is on the line.

Our Saint needs to rely on these people for everything right now. Realistically, what would she even be able to do if she were to leave? Now if Kondou had some kind of magic, that would be a completely different story. He'd be able to protect her, help her survive in this new world, and would be more likely to side with her than literally anyone. Though that would only really work if the tag along was someone other than Kondou and even then it would be iffy... he'd probably see it as more efficient to just put up with helping this country until their magic research either turns out well or fails.
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