The RP that I've been doing with a core group of friends (with various other players coming and going over the years) started as a Shinra Inc (Final Fantasy VII) clan back in the early 2000's. At that time, it was centered around a combination of RP fighting and a continuation of the FFVII story (this predated Advent Children by several years). We eventually ended up incorporating elements from other games that we liked, most notably Xenogears, which eventually took over as the main overarching plot, with the FFVII element essentially becoming a mere "chapter" within that broader universe (which we have since added and expanded upon in our own ways - and in fact, one of the primary architects hasn't even played Xenogears yet, lol). After a couple of years, we got bored of being Shinra, so we staged a big IC event where the company got destroyed from the inside and we took our characters and formed a new group - the Yggdrasil Space Pirates - which went on to jump from forum to forum joining in on various interconnected RPs while still maintaining our own core narrative and intermittently staging our own major plot threads whenever we felt like it. Again, allowing random newcomers to join up as we went along. People were free to come and go with original characters or fandom-based characters as long as it didn't directly contradict or otherwise interfere with the main story that we had going on. We're still at it, though it's slowed down due to adult responsibilities obviously taking priority. Point is, it doesn't matter if it's "original" or "fandom" or some combination of both. What matters is that you enjoy it enough to stick with it. And if you're actually doing a good job, other people will want to get in on the action too, even if only for a chapter or two.