Their ability is getting more and more ridiculous. If they tried, they probably could take someone's ability to breath automatically.
Nah, she can only affect things related to the other side. In this case, it's not his faith in general, but his faith in Urumi. The way that girl's ability works is probably something like making people have complete an total faith in her, or something. Or Sorowa was just guessing.
Regardless, all they removed was what Urumi forced on him with her ability. He's sad without it because it feels good to have something to devote yourself to. And now he doesn't have that anymore.
I bet this guy goes with them and tries to get Urumi to brainwash him again, but it doesn't work anymore.