Translation: shell boy
Habitat: decorative shell boxes
Appearance: Kaichigo is the spirit of a shell box come to life. It takes the form of a small, doll-like boy in a kimono.
Behavior: Kaichigo haunt the shell boxes used to store beautiful and expensive painted shells. They come out when nobody is around and play with the shells, flipping them over and moving them around into different positions.
Origin: Kaichigo’s origins lie in kaiawase (“shell matching”), a popular Heian period game which uses painted seashells. Beautiful shells of the right size and color were collected and decorated, their insides lined with gold and painted with scenes from popular stories, such as The Tale of Genji. The two halves of the same shell would be painted with the same scene, and players of the game would try to match the two sides. Beautifully decorated shell boxes, or kaioke, were used to store the shells while not in use.
Kaiawase gradually became replaced by other matching games, such as karuta, which use less exquisite playing pieces. The kaioke and shells themselves came to be viewed as precious art objects instead of toys. Because each shell half will perfectly fit its matching half and no other, expensive kaiawase sets came to be used as wedding dowries—symbolizing a perfect and unique match between bride and groom. Some boxes have been passed down from mother to daughter over and over for centuries. Those kaioke which have been around for a very long time and are no longer used as games begin to resent their existence. They grow restless and want to be played with once again, and develop a soul: the kaichigo.