People sometimes ask me for sightseeing advice for Ishigaki. I always answer: “Taketomi island!”
This small island is just a short ferry ride away and it’s such a beautiful place with the most relaxed atmosphere. I wouldn’t suggest that you go here to actually do anything more than slush around in your flip-flops and enjoy the scenery. I usually walk into town, have lunch and then head out to one of the white beaches, maybe go for a swim or snorkel.
I’ve never stayed overnight but I heard that the west pier is a really good sunset spot.
If you are on a pressed schedule, you could probably squeeze a visit in with some other activities. But that would be missing the whole point if you ask me ^_^
You can read more about Taketomi here: http://visitishigaki.com/nearby-islands/taketomi-island/