Kaichigo' refers to a type of Japanese spirit appearing in "Hyakki Tsurezurebukuro Hyakki Tsurezure Bukuro' (One hundred bags in idleness), collections of ghosts, spirits, spooks and monsters, described by Sekien TORIYAMA. Tsukumogami (the spirits of discarded object) of 'Kaioke' (a bucket for clamshells).
kaioke' is a kind of bucket used to keep clamshells for 'kaiawase' (a Heian period game which involved pairing the two parts of clamshells) or 'kaioi' (an old name of kaiawase game in the Heian period, which involves pairing the two parts of clamshells) played from the Japanese medieval period to the Edo period. In the book, a person who seems to be a child crawling out of the kaioke was described. The explanation says, 'I think this kaichigo must be a brother of 'hoko' (a baby doll charm) in my dream'.
Sekien suggested that kaichigo might be a brother of hoko, a baby doll on its hands and knees, used as a lucky charm for little children. Today, kaichigo can be interpreted in a couple of ways.
One interpretation is that; as people got tired of playing the game, clamshells that became useless turned to be a spirit. Another one is that; kaichigo was born from an old kaioke which had been handed down from a mother to her daughter as marriage furniture. Since kaioke was considered to be one of the best appropriate marriage furniture and passed on from parents to their daughters, it was common that these kaioke were used for hundreds of years from generation to generation. However, there is no reliable oral tradition that the kaichigo actually appeared, therefore, another interpretation indicates that it was a imaginary creature Sekien made up.