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I just wanted to know if nobodies were going to be included in the rp. Are they going to be enemies or can created characters be nobodies? Like Organization 13? Just wanted to know.

It depends. Nobodies, thus far, have been quite complex. And lacking extreme emotion, they don't tend to care about others.

But there have been benign nobodies. At the moment, the RP's story is set to begin beween KH1 and KH2, exploring the time-gap left from the nobodies' interference in Chain of Memories. Nobodies are already a complex existence (non-esixtence?), so fitting them in with continuity contraints is also difficult.
Needless to say, you can't just make a character a Nobody without consulting the crew first. But it would be an interesting idea to create a Nobody born of another character who'd previously lost their heart.

I do have an interesting idea I'd like to run past you guys, see what ya think. But not even I'm sure where it belongs right now, lol. Either here, or the plot/characters thread.

They wouldn't necessarily have to save a "character slot" since the maximum is only three active at the same time. But I don't reccommend playing three at once.
Stats and inventory can easily become disorganized, especially for those who tend to use the same kind of character each time.

The real question is, if a person is allowed to portray a previous character's nobody, how does the nobody start? Will they begin at level one or closer to what the character was before? Will they have the same stats? How were they made in the first place - regular nobodies or a rare anomoly like Roxas and Namine? Will they intereact with other nobodies?

In spite of potential difficulties, nobodies have great potential for interaction. Xigbar of Organization XIII has met keybearers apart from Sora, and his life as a nobody was relatively short; and since Xemnas seemed to know far more about hearts and keyblades than his heartless counterpart, it's reasonable to assume he and other Org13 members have also.