Kai-oke lacquered containers are available in various shapes and were used to store shells of kai-awase (shell matching game). A popular game in Japan from the Heian era (794-1185) to the end of the Edo period (1868). The shells were of a species of clam called Hamaguri which had the unique characteristic that none other than the original pair would match together. 360 shell-halves would be divided between two groups of players. Each side would put forth one shell and when the opposing player would find a shell to match his, he won that shell.