One common theme could be redemption. Ulysses has a complex past, and in relation to the female courier, there might be a story of him finding some form of redemption through their interactions. Another theme could be trust. Given their different stances in the game world, building trust between them can be an interesting plot point.
Well, finding good fnv ulysses x female courier fanfiction can be a bit of a hunt. You could also check out some Fallout New Vegas - related forums. Sometimes fans share their own written works or point out great fanfictions in the discussions. It's possible that within those communities, you'll come across some stories that focus on this particular pairing.
One of the best FNV (Fallout: New Vegas) companion stories is Boone's. His backstory of being a sniper in the NCR and his tragic past with his wife makes for a very engaging narrative. It adds depth to his character and his actions in the game.
I still don't know what 'fnv' is exactly. It could be a new thing that I haven't heard of. Maybe you can start by saying if it's a brand, a fictional entity or something else.
Well, 'The Courier' is purely fictional. The plot and characters were imagined by the writers for entertainment purposes. There's no real-life basis for it.