I saw this post and wanted submit my OC driven story from my Star Wars fic, Hearts of the Empire. The OC, Jordana, is a close friend of Anakin Skywalker and ends up falling in love with him. He'll eventually fall in love with her as well, which I guess puts her dargerously close to Mary Sue territory. The thing is that it takes many, many years and plot points before the relationship developes. Even though the story does focus on the relationship, it also has a plot as well.
It's posted at FF.net (link: http://www.fanfiction.net/s/2405115/1/). There's also a completed version here on AFF, but I decided to re-write it, so the one in the link will be the final version. There's also two planned sequels for it as well.