Kumejimakaigan no Tatamiishi (the Tatami Rocks of Kumejima Island Beach) is a coastal area of Oujima Island, Okinawa, that features regular formations of peculiar rocks.

Oujima is a small isolated island lying to the east of Kumejima and has a circumference of only 4km. On its southern end are groups of peculiar pentagon- and hexagon-shaped rocks about 1m to 2m in diameter. These smooth rocks are called tatamiishi (tatami rocks) because the appearance of the rocks is similar to traditional Japanese flooring with tatami mats. At a glance, they also look like the patterns on a tortoise shell.

Ou means the isolated island where 'fusou' (a ritual where the deceased were left on an island to naturally decompose) was practiced. Oujima was once deserted, but today is used for sugarcane-growing.

The only highlight of this island are the tatami rocks. The beach has also become a popular spot for swimming.

There are about 1000 tatami rocks, each approximately 1m in diameter. These rocks were formed when hot magma cooled and cracked perpendicularly to create a pillar-shaped structure. It is very rare, even outside Japan, to see so many of these rocks in one place.

Raden is a decorative technique used in traditional crafts. The Raden kashiki (Raden sweets bowl) is one example of traditional Ryuyku lacquerware.
   The craft of Raden-work involves a technique of framing and pasting the pearls of turban shells and abalones, then adjusting and grinding them into patterned shapes on a lacquer-coated surface. This technique comes from a decorative technique where light is beautifully reflected in blues and whites. The lacquer-coated surfaces are carved in patterns, while the shells are fixed with lacquer paste to the surface. Some Raden-work features engraving on the shell itself as decoration.
   Raden includes decoration not only using shell, but also using amber, tortoiseshell and pieces of metal. Decoration using gold and silver is not called Raden, but Hyoumon or Heitatsu.
   Raden kashiki is one example of Ryukyu lacquerware that developed uniquely from earlier lacquerware techniques introduced from China.

Edo Bekko is a tortoiseshell handicraft made in Tokyo, applied to eyeglass frames, gold-lacquered objects and carvings.
   Bekko has a long history: a biwa (Japanese lute) preserved in the Shoso-in imperial treasure house (dating to the C8th AD) features the shell of a hawksbill turtle. In the Edo period, more sophisticated gluing techniques led to more complicated effects using bekko.
   Hawksbill turtle shell is the main material for Edo bekko, and is used to make a variety of stationery items and accessories.
   Hawksbill turtles live in the vicinity of the equator and can measure up to 180 cm in length and 200 kg in weight after 50 or 60 years. The number of shells is always 13; the transparent part, which comprises only 10% of the shell, is treasured, the other parts, which are black, are called 'fu'.
   Edo Bekko is a very valuable and graceful craft.

Among the tribute that Ono no Imoko, an official envoy to the Sui court, brought back to Japan from Sui in 608 was an art object in which tortoiseshell was used. In Shosoin (the Imperial storehouse), there are also some tortoiseshell products brought into Japan in the same period. The technique of tortoiseshell work was introduced from China in the early Edo period. Later in the Genroku era (1688−1703), tortoiseshell began to be used to make accessories for high-ranked yujo (the prostitutes) and wives of daimyo (domain lords). With the flourish of Edo chonin bunka (culture of townspeople), a lot of tortoiseshell was used for personal items such as kanzashi (hair ornaments) or combs. Since then more complex techniques of carving, makie (gold and silver powder), and zogan (damascene) were developed. Tortoiseshell materials are made from the shell of the hawksbill turtle, the shell of which is up to 1m long. The shell is pressed flat and cut out into panels of appropriate sizes, then the panels are pasted together. At the present, Tokyo, Osaka, and Nagasaki are the three largest centers for tortoiseshell work. Osaka is known for fine carving techniques such as openwork and its main products are brooches and other accessories.