A few years ago I wrote a fan fiction which was almost entirely composed of OCs, with the occasional cameo of minor characters - it was more about using the concepts of the original story than using its characters or plot. I have one similar idea for a different fandom if I ever get round to writing it. But the majority of my ideas do include favourite characters.

That's actually really cool. I've never thought about writing a fic about the concept of the original content rather than the characters.

At the time, I think that's what I actually thought fan fiction was. I can vaguely remember being surprised/shocked at how many fan fictions were centred around canon characters and ships.

Still pretty cool though. :P I was very much the opposite; I didn't realize that OC's and self-inserts were so popular.