The Nansei Island Group including Okinawa and Amami are formed of beautiful coral reefs. The abundant sea life of the area facilitated the use of shells for making products such as knives, axes, and necklaces.
The shells and shell work produced in Okinawa was transported north along the warm Kuroshio current and even reached the mainland of Japan some 2,000 years ago during the Yayoi Period. This has been called "The Shell Road" and is a trading route from the Nansei Island Group northward to the north of Kyushu, past the inland Seto Sea across to the Kinki region of the Japanese mainland. The other route on this Shell Road was up the seacoast of Japan via the Genkainada area off the coast of Kyushu.
Recent excavations in Hokkaido, the northernmost island in Japan, have uncovered shell decoration made in the South Seas, a distance of over 2,000 kilometers. The raw materials, mostly Tricornis latissimus and Conidae shells, were transported to the northern part of Kyushu and shaped into shell products and shipped out all across Japan.
That such a magnificent trading operation was being conducted in the Yayoi is credit to the stable economy of the era and potential for a division of labor that backed it up.
Trading was active along the "The Shell Road" for over 800 years from the Yayoi period (200BC - 250AD) through to the Kofun or Tumulus Period (250 - 552AD). In the Kofun Period the trade brought an increasing variety of shell to the mainland of Japan and the people of Okinawa received grain, products made from metals, and cloth.

The Shell Road