Japan's Ryukyu Islands, also known as the Nansei Islands, are a chain of islands that stretch from the southern tip of Japan to Taiwan. Large, oval 100 mon coins where cast there between 1862 and 1863. These are somewhat more rare than other 100 mon Japanese coins that look the same, but the inscriptions are different.
Typical catalog pricing runs like this:
worn: $30 US dollars approximate catalog value
average circulated: $125
well preserved: $250
Of course, with any valuable coins, fakes are possible. Western folks are used to round coins, so the oblong shape with square hole catches the eyes of tourists. Modern-day entrepreneurs create nice-looking reproductions and sell them like hotcakes! From a coin collector's point of view, the tourist coins have no value.