Hajime is 100% going to rebuke the devil. Not because he doesn't have a lot of issues to work through, but because he isn't going to trust a strange voice over the radio. He'll also be pretty open about this distrust, and once he starts seeing the actual physical results he's going to go out of his way to try to dissuade people from listening to it. SO if you're looking for someone to actively try to prevent your character from letting the devil in, Hajime is your dude. Your very tired, very suspicious dude.

Once more details are made clear, he'll also be more than willing to actively fight against it as well. He can't actually like, do much, being a normal teenager, but he's definitely willing to try.