Kamishibai are small-scale, informal, intimate theatrical performances put on in the old days in the street for passersby, particularly for children. These days there's no telling where and when you might run across a kamishibai in the street, although certainly your chances are better in the more traditional neighborhoods like Ueno.
You will be attracted by one or two fluttering banners, the rhythmic clapping together of two pieces of wood, and the ritual bawled-out announcement to the passing crowd that "The kamishibai is about to begin!" Sometimes there will be other attempts to attract a crowd, such as a familiar tune on an unfamiliar instrument like a clarinet, a juggler, a magician, or a contortionist.
A rug will be laid down for the kids, who may be offered a piece of candy to come and make themselves comfortable. (In the old days, the kids would have to buy their candy for a few yen and this would entitle them to a front seat.)
Kamishibai stories are narrated using a series of emphatic illustrations on boards the size of the screen of a small TV. The narrator uses different voices for the different characters and the children are drawn into the story: "Should the squirrel run away and hide or should he stand and fight?" And the story will go the way the children suggest.
There will be stories of an evil Santa Claus, of the adventures of a peanut that can jump very high and change colors, of a team of bumbling robbers who of course get caught, of floods and of fires. There might be the story about a boy with a great curiosity about everything who sneaks aboard a sailing ship and climbs to the top of the mast--dangerous--and there is a storm and he has to jump off into the ocean--SPLASH--where he is rescued by kindly fishermen who tell him it is a fine thing to be curious but he must be careful and not cause other people trouble.
A kamishibai story takes maybe ten minutes. There will be maybe twenty pictures and a dozen different voices.
Kamishibai these days evoke nostalgia for the immensely popular street kamishibai of the past, which were performed by professionals, that is, people who lived off what they did. Most present-day kamishibai are aimed at adults and are not held on the street but in small halls, where they can be illuminated and microphones can amplify the sound. They recall rakugo monologists without pictures. Not the same thing.