Flights from Darwin to Naha lean towards being more expensive in January. Prices are generally better when you fly from Darwin to Naha in May, with the cheapest ticket starting at $461.
When travelling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in Darwin is roughly greater than that of Okinawa. You can assume this to be the case over the next 23 days.
With an average temperature of 34 °C, peak weather can be found in October. As a traveller, expect to see changes in flight prices during that period. The temperatures in Okinawa are colder than in Darwin.