Miyakojima is a fantastic destination if you want beaches and crystal clear water. It’s a mostly flat island with sugar cane fields everywhere, and there is not much to do if you don’t like swimming – but if you do, please go. A bike is a must have, or a rental car/scooter. The food is great, the weather is great, the sea is perfect, and you can find vending machines in the middle of the jungle if you ever doubt you’re still in Japan. I highly recommend snorkeling at Yoshino Beach, which features a sort of natural “pool” of coral reefs due to the geography of the beach – fish gets “trapped” because of the largest reef so they stay close to the beach and it creates a natural aquarium.
There is also a gorgeous lagoon that is very high in salt so you float pretty well in it, and if you walk in the water you’ll find little hidden beaches everywhere.
There are direct flights from Tokyo and Osaka, and some flights have a stopover at Naha airport.
The dangers would be sharks and jellyfishes – other nasty things like cone snails shouldn’t be there but it’s an almost tropical island in the Pacific Ocean, so you can never be 100% sure. If you swim where there is no net, wear shoes and check the flags on the beach. There are no Habu snakes on the island. You can, and will, encounter absolutely massive spiders (Jorō spiders, used for their silk). They’re pretty chill but they can bite. They’re literally everywhere. You can’t go to Miyako and not see them.
I had a lot of fun there and I highly recommend giving it a try.