You almost certainly don't need to get a visa in advance for Japan, unless you're staying more than 90 days, but it depends on your citizenship. See
Japan Visa Information for specifics.
Okinawa is a lovely place once you get outside the cities (Naha, et al), so I hope you'll get a chance to see some of it. For that matter, I'd recommend including a stopover in Tokyo en route so you can do some sightseeing there, too.