Hey. Glad to see another interested player in the forum
More players are always welcome.
However, I do have to say, if you're unsure of whether or not a similar RP has already been made, a good idea would be to actually browse the forum? It's only three pages long, and practically all threads except the top 5 threads are dead (as you can see by the last post dates). Also, another good idea would be to read the forum rules (
here and
here), which among other things mention that
1). To start a new open roleplay, you must have actively participated in other roleplays before, and
2). That the idea must be fleshed out. Look at the first posts of the other roleplay threads; they're far, far more elaborate than just "you can be any Sailor Moon character or even a new one". You need to describe a plot, rules, a setup, the basics of the game, and so on and so forth.
Your message would have been better off posted in the
Brainstorming/Planning thread, both in regards to you wondering if someone has already done this, as well as to see if any players are interested.