Yes, a couple of years ago
Took a flight to Tokyo then domestic to Naha airport
If I'm not mistaken, you can get there via Taiwan on a ferry (you'll notice a lot of Taiwanese tourists especially at the shopping areas and what's purportedly one of the largest DFS malls), or if adventurous there's also a loooooooooooooooooooooooooong ferry ride from Tokyo itself
I find it rather odd that you'd decide to go without a plan ... if I may ask, why choose Okinawa?
Yes, but English has much better mileage than the mainland, possibly because of the US military base
Not uncommon to see GIs around, with shops that pander to them - food, bars, even military supply stores for those who may have lost a dogtag or two...
It's distinctly different from the rest of Japan, which could be good or bad depending on what you went there for
For e.g. it has a tropical island town vibe and feel, where everyone's always on a laidback holiday; there's less Japanese-y stuff, more Okinawa
Sushi and sashimi less fresh, different fishes, salmon's hard to come by, irabucha sashimi's weird
Okinawa ramen tastes like a distant relative of fishball mee, there's stuff that's not available elsewhere - taco rice, A&W, Blue Seal ice cream
The sounds of the zanshin and yelping singer in every store
There's sugarcane juice machines and drinks, something we find common here in Sg but unique here, the cost reflects it
Shisa's line the front of almost every door, home or business, those without probably a non-native
It's a beachcomber/watersports lover's paradise
Being neither, I found the Ryukyu culture fascinating, most everyone embrace it and sometimes unfortunately try to sell it in the most kitschy wasy as possible
Why not consider Kyushu. Many more places to go for the time you have. The south-east part is very tropical in nature; like Okinawa.
Okinawa main island is not a big island.
Direct SQ flight landing in Fukuoka on Kyushu.
Can easily access to different part of the island by JR and also the southern part of Honshu too (include Yamaguchi, Himeji, Hiroshima and Miyajima)