Kai-awase is a game that originated in the Heian period and remained popular among the aristocracy until the Edo period. It involved high-quality materials and cultural sophistication, limiting it to the upper class.
The game used pairs of painted clam shells (hamaguri), featuring scenes from The Tale of Genji, like Ukifune, Kagerō, and Kashiwagi. Players would split into two teams and compose waka poetry. The shells were divided into two groups: one half held by players (called debei) and the other placed face-down on the ground (jibei). The goal was to match the correct pairs, similar to modern memory games. Winners were rewarded with prizes and a banquet.
In the Edo period, craftsmen expanded the themes to include poetry from Hyakunin Isshu. Tokugawa Reimei-kai even produced limited Genji sets in 1980, each featuring 54 pairs—much fewer than the 360 of ancient sets. The craftsmanship was remarkable, as shells could perfectly match any counterpart.