The unnamed crescent-shaped island on which the Storyteller Girl lives is the main setting of Tsuki no Sango.
Characteristics
The island is a small colony of less than fifty people. There is no port, and on the beach is a coral reef unique to it. For the people living on the island, the coral reef is a part of everyday life, but for the people of the mainland, it's more valuable than jewels.
Since around the time of the Storyteller Girl's grandmother, this island has been treated as a sacred ground. It is absolutely forbidden to enter by sea, so only the privileged who own an aircraft are able to come. The island is seen as special, with people of the mainland seeing as the star of hope for the restoration of humanity.