Hermione would probably be very interested in learning about the religious aspects of the church. She'd start reading any religious texts available and try to understand how it all fits in with the Muggle world. Ron, on the other hand, might be a bit more uncomfortable. He's used to the wizarding world and all this Muggle religious stuff would seem a bit strange to him.
Well, he might be quite confused at first. Churches are not really a part of the wizarding world he's used to. Maybe he'd be looking around in wonder at all the religious symbols and the way people pray.
Well, Harry could be really confused at first. Ouran is a very different world from Hogwarts. He might be shocked by the opulence of Ouran Academy and the strange club system there. Maybe he'd try to find a way to fit in while still being true to his wizard self.
He might meet international aurors. These are highly skilled wizards from different countries who are experts in dark wizard catching. They could teach Harry some new combat spells.
He could meet Fleur Delacour's family. Since Fleur is from France, her family might be an important part of the French wizarding community that Harry interacts with.
Hermione would be a likely companion. She loves learning and exploring, so she'd be eager to go on a traveling adventure with Harry. Ron might also tag along, especially if there's a chance of food and adventure. Neville could be another option. He has grown a lot in courage and his knowledge of plants could come in handy in different magical environments. Luna Lovegood would be a very interesting companion too. Her unique perspective on magic and the world would add a lot of fun and mystery to the journey.
Harry could meet some local magical creatures that are unique to Africa. For example, there could be a magical creature similar to a hippogriff but with different characteristics. And he may also meet African witches who are experts in herbal magic, which they use to heal and protect their communities. They could teach Harry some of their techniques and knowledge.
It could be really interesting. Maybe it would show a character in the Harry Potter universe who is also part of a church community. They might struggle to balance their magical life with their religious beliefs. For example, they could wonder if using magic goes against the teachings of their church.
I'm not sure specifically about a 'Harry Potter Member of the Church' fanfiction. There are countless Harry Potter fanfictions out there, but this combination might be a bit rare. You could try searching on major fanfiction websites like Archive of Our Own or Fanfiction.net using those exact keywords.