The premise of the game would be much more 'open world' than 'closed group', using a system I'm adapting from the Billy vs. Snakeman Naruto-parody game:http://www.animecubed.com/billy/?Felina
(if you play look me up, I'm Felina there). For the uninitiated, the system is a sort of extension of what you might see in Persona 3: a major factor is time-management, choosing how to use the time available to your character in the day, whether it be socializing with other ninja to make allies, completing missions to gain ryo, training in abilities and jutsu, or pursuing personal goals.
This part of the game would run in a semi-autonomous, quasi-realtime fashion. Basically, all active players would get a certain number of 'actions' they could undertake per day, and how they use them would both describe the day-to-day life of their ninja, and determine what sort of items and stat bonuses they have available when they undertake the other side of the game: special missions.
Special missions would be handled in a more traditional 'adventure' format, in non-realtime. They would be for significant events, like a Chunin Exam, an invasion of a village, or major personal events for individual characters. This is where the 'meat' of the game would be, with the day-to-day play being more to give people something to do during the oft-times slow pacing of forum play.
Players would be able to create their own character or play some of the canon characters (the general rule of thumb is you can only play those who start as Genin in the first season of the show). The main story would mostly follow major group events like Chunin Exams, village-vs.-village matters, etc. As with the show, it would mostly provide a backdrop for the individual stories of the characters. Players will not be a 'team' by default, but will be able to team up if circumstances warrant it, but may even end up opposed to one another at times, or forming competing teams. (Particularly during an Exam.)
There would be an odd mix of system RP (special missions) and freeform RP (PCs who are teamed up are always free to play out 'downtime' type scenes together, or with other PCs from their village). The system would be almost completely original; it's based heavily on the very simple Billy system, but with a few tweaks to add more player control and choice into the mix. It will be quite easy to learn, however, with most actions being determined by rolling one of three attributes (Genjutsu for deceiving with illusions or intelligence based tests, Ninjutsu for using ninja elemental magic or skill-based tests, and Taijutsu for hand-to-hand combat or physical tests) against a difficulty number with a certain number of necessary successes.
The game would begin after I return from the Country Hidden in the Sands to the Country Hidden in the Recession. That's December in people-time. I'm mostly gauging interest right now, though if people are up for it we can start getting characters thought up.