Kaiawase (shell-matching) (貝合わせ)

Kaiawase is a traditional game from the Heian period. Originally, kaiawase was played among nobilities as a kind of awasemono (games in which people gather each bringing something of the same kind to decide which is better) in competition for the beautiful coloring, shape, and rarity of the shells, or the superiority of uta (poetry) composed with the shell itself as its subject matter. On the other hand, kaiawase as a game similar to the card game 'Concentration' used to be called "kaioi," but it later became mixed up with the other one because of its hand movement of putting shells together, and came to be called by the same name of kaiawase.

How to play kaioi
The shells used for kaioi were clams caught in Futami, Ise Province, which were suitable in size for women holding in their hands. A piece of paper was pasted on the inner surface of the shell, on which they drew a picture on the theme of Genji (The Tale of Genji) or the like, then finished it up with gold leaves and others to give it a brilliant coloring; the same picture was painted on each shell of the pair.

When the shorter ear of the shell faces you, if you turn the umbo toward yourself, dashigai (clamshells which are put in the bucket and later taken out one by one to play kaioi) as yin (passive) is on the right, and jigai (clamshells which are placed on the mat in kaioi) as yang (active) is on the left. The pair, which represent heaven and earth, and are also compared to man and woman, were stored in separate kaioke (a bucket filled with clamshells). The rules of the game were developed with reference to the study of astronomical almanac and others.

Jigai as heaven are put inside down, starting with 12 of them in the center representing 12 months, then 7 shells as the days of the week are added, and finally, exactly 360 clamshells representing the days of a year are arranged in 9 rows.

It is said that 9 rows are based on old-time astronomy in which heaven were considered ninefold.

Starting with 12, then 19.

19 is the important number in the study of calendars, and both the solar and lunar calendars take 19 years to complete a full circle.

When all jigai are set, nyobo (a court lady) as dashiyaku (a person who picks out dashigai) takes one of dashigai out of dashigaioke (kaioke for dashigai) and put it inside down on the center.

More than 20 himegimi (daughter of a person of high rank) surrounding the shells try to find only one jigai, out of 360, with exactly the same spots and shape as dashigai. Someone calmly takes up a pair of clamshells in her hand, and if they match perfectly in one hand, she separates the pair and put them inside down in front of her knees.

Then dashiyaku put another dashigai on the center and they repeat the same thing again and again, and the player with the most shells should be the winner.

Because making many mistakes in the game were considered shameful, kaioi became a means to learn morals and kaioke had been one of a bride's household articles in high society until the Meiji Restoration. Kaioi has not been played anymore in and after modern times, and now a real, complete set of kaioi can be seen only in museums, but some hinaningyo (a set of dolls displayed for the Girls' Festival) still has miniature kaioke and other articles.

Kaiawase in the Edo period
For kaiawase in the Edo period, they used clamshells with makie (Japanese lacquer sprinkled with gold or silver powder) or gold-leaf decoration inside. Bivalves such as clams would not match any shell other than their counterpart, so people played kaiawase choosing a pair out of the shells placed face down.

Because the shells did not change their partner, they became a symbol of conjugal harmony. Kuge (court noble) and Daimyo (feudal lord) family prepared beautiful kaioke and shells for their daughter as the bride's household articles. On the inside of a shell, natural features or a court couple who looked like the Tosa clan were often depicted. A pair of shells carried a matching pair of pictures.

Octagonal kaioke filled with beautifully decorated awasegai (shells for kaiawase) were made in pairs. They were the most important article of the bride's household effects for a daimyo's daughter, so that they were carried at the head of a wedding procession.

After the procession arrived in a bridegroom's residence, 'kaioke watashi' was conducted as the first ritual, in which kaioke was handed over from the bride's side to the groom's side. Karo (chief retainer of a feudal lord) or other senior vassals performed kaioke watashi as the most important ritual in a wedding ceremony of daimyo families.