To start, the couple running the place AND two of their guests came to pick me up from the airport (500 yen), and we had a fun ride back to the house. They cooked delicious meals for dinner (800 yen), and at night we went out to look at the stars. On my first full day, I asked about snorkeling, the hosts organized a tour (2500-4000 yen), two other guests joined, and we had a lot of fun swimming with reef fish and a few sea turtles. That evening, after dinner, a neighbor came over, and the hosts pulled out some plum wine to greet him. Everybody was very friendly and had a great time.
The small Kurima island is completely walkable, there are sand beaches on the West side, and a few restaurants in the village, just two minutes walk from the guesthouse. To go anywhere else, it helps to have a car or, in my case, make friends with other guests and let them drive you around. It's easy to make friends sitting at a big round table enjoying a home-made meal at dinnertime.