A persona who becomes a kannagi can see the supernatural at any time and in any place. The other option, kamikakushi, lets anyone see the supernatural, but only sometimes, and only in particular places. “Kamikakushi” means “hidden by the kami”, and could be translated “Spirited Away”. Indeed, the Japanese title of the Miyazaki anime called “Spirited Away” in English is “Sen to Chihiro no Kamikakushi”: “Sen and Chihiro’s Kamikakushi”.
In kamikakushi, a kami takes a number of people out of the mundane world, and into a separate world inhabited by the kami. In this world, any human being can see kami and communicate with them directly, and the kami can, and do, use obviously supernatural abilities.
Only kami can initiate kamikakushi, at least to start with, and it takes a significant amount of effort. The more people a kami tries to spirit away at once, the more effort it takes, so small groups are more common. It is not normally possible for the kami to keep someone in kamikakushi indefinitely, and it is not possible to take anything from kamikakushi to the mundane world that didn’t get there from the mundane world first. Time normally passes more quickly in kamikakushi than in the mundane world, so that even someone taken for a long time is only missing for a matter of days, at most. This, of course, makes it very hard to convince anyone else of what happened.
In addition, there are many kamikakushi, all of them different. Most of them look superficially like Japan at different periods of history, from primeval woodland to the present day, but the inhabitants and events of each world are different. This means that the accounts of people who have been spirited away do not agree.
The first session of a kannagara game, then, would typically involve kamikakushi, to get the players involved in the supernatural side of the setting, and give them a chance to talk directly to the kami of their jinja. After that, the personae can only return to kamikakushi if they can give the kami enough strength to take them, and convince him that it is a good idea. These goals play into the themes of Kannagara.
Kamikakushi also provides an opportunity to have pseudo-historical game sessions, when the personae visit a kamikakushi that resembles a period of Japanese history. The kamikakushi is not actually Japan in that historical period, so not all details are the same, but the overall culture and atmosphere is preserved. This is important, because it allows people to run game sessions without doing an inordinate amount of research.
Not all game sessions take place in kamikakushi, so gaming groups must choose how often they go there. If it is very rare, the game will feel more mundane, but the wonder of kamikakushi will be easier to preserve. If it is very common, there will be more supernatural events, but they will become commonplace. At the moment, I think the default will be that kamikakushi is rare to begin with, but becomes more common as the story progresses. Once the characters have become kannagi they can, of course, see the supernatural in the mundane world as well, and this may well make it easier to enter kamikakushi.
Kamikakushi may be linked to one another, and may also be linked to the actual past, as opposed to supernatural re-creations thereof. That, however, is something for the future development of the game. Initially, each kamikakushi will be self-contained, and fairly small. Links to other kamikakushi, other places, and other times can be discovered or created in play.