The shells are those of the hamaguri clam of which only an original pair will fit together. They are used in the game of Kai-awase, which involves matching the shells in pairs. The game was popular amongst ladies of the court in the 13th and 14th century and the shells for the game were kept in a pair of lacquered kaioke [shell boxes]. It was because of the unique fit of each pair of shells, they were thought to be auspicious on the occasion of marriage in important families. A set of Kai-awase, in its kaoike, traditionally led the procession bringing the dowry of a bride to the house of her intended.