That saint at the beginning could be an interesting character, and I could see her interactions with the MC's people going a couple ways. Considering she wiped out the monsters for hurting people, there's a chance that the MC could convince her they are not an enemy. He's only helped people so far, after all, and he has no plans to go around conquering others.
On the other hand, I could also see her try to attack him on sight. She may just see his shadowy form, and attack thinking he is some abomination against her diety.
Hopefully, he gets the chance to build up a bit, and then announce his country's existence with letters or envoys. That way, he would have much more control over how he's seen by outsiders, compared to if he was found by a spy or explorer.