Lol, I think I'm in over my head a little at this idea, but I can't shake it either, the idea has so many cool ways it could go and the more I'm expanding upon it the more I'm excited to write a story like this. If I can ever complete it, it may just be my longest story to date.
It is based off the Harry Potter books, however in this case it is not at all connected to the main story of Harry, Hermione, and Ron. It will intersect with their story some, but not much, so it will be a story from years 1 through 7 of a OC character that is 2 years older than Harry, Ron, and Hermione. So yes this is an OC character who will be in the same year as characters like Lee Jordan, Angelina Johnson, George Weasley, and Fred Weasley. And yes I do plan to involve a rather unexpected romance later on into the story vin their 5th year, but I haven't even gotten to the point that the OC started her 1st year at Hogwarts yet, so this is going to be a while before I like the story enough to begin releasing chapters, I've still got a lot to clean up and flush out in the story before we get to that point, but I'm hopeful as I really think this would be a cool story.