A “yorishiro” is a temporary vessel for kami. They are used when a matsuri is being conducted away from a jinja, where the goshintai (“honourable kami body”) is a permanent vessel for the kami. The scholarly consensus is that in the earliest days of Shinto there were only yorishiro, and that permanent goshintai became part of normal practice around the time Buddhism started to spread in Japan, probably as a result of the influence of Buddhist temples and images.
Historically, yorishiro appear to have included trees, rocks, and people. There is extensive archaeological evidence from the earliest jinja for the use of rocks as yorishiro, and it seems that some of the largest developed into goshintai. That is, it seems that people came to believe that the kami was permanently present, rather than simply visiting for the matsuri.
The use of people is, obviously, not attested by archaeology, but there are numerous references in myth, and there are survivals in matsuri that are still performed today, for example at Miho Jinja in Shimanë Prefecture.
However, these days the most typical yorishiro is a version of a tree: a himorogi. A himorogi is a large branch of sakaki (an evergreen tree closely associated with Shinto), with a large number of smaller branches coming off it, so that it looks like a small tree. Shidë, strips of white paper folded into lightning bolt shapes, are hung from it, sometimes with strips of linen or other fabric, or other decorations. Such himorogi are used at jichinsai ceremonies to bless a building site, and one was used in this year’s Gion Matsuri procession in Kyoto, as I discussed a couple of weeks ago. The simplest version of this is a gohei, which is a simple wooden wand with two shidë attached the top. This might be used in a matsuri being conducted inside someone’s home, where there is not space to set up a full himorogi.
A couple of weeks ago, Jinja Shinpō carried an article describing a traditional matsuri at Takasë Jinja in Toyama Prefecture, where they used a very unusual yorishiro.
The matsuri itself is said to have started in the late seventh century, and combines prayers against insects that eat the crops with prayers for a good harvest. This year, prayers for the end of the pandemic were added. People visiting the jinja from early April were encouraged to write their names and prayer for the end of the pandemic on a wooden slat, and leave them with the jinja.
The unusual himorogi is a sacred fire. This is kindled during the matsuri itself using a friction drill, and then transferred to a brazier in the jinja precincts. This year, a further norito was read at this point, and the wooden slats with prayers on were burned in it. The following day, the fire is normally transferred to a mikoshi and carried around the area, but this year the priests simply carried the flame itself around, as a himorogi.
The article reports that, in 1879, there was a particularly bad insect infestation, and everyone from the village attended the matsuri. The sacred flame was handed out to everyone, and placed at the fields to drive away the insects. That year’s harvest was, in the end, a bountiful one, so the village held a special thanksgiving matsuri in the autumn.
This is the first time I have come across a fire used as a himorogi. Fire does not normally play a significant role in Shinto ceremonies, and although the metaphor of lighting one candle from another is a common way to explain what happens when the kami of one jinja are enshrined at another, I had not previously seen a literal example.
This sort of case is the reason why it is very hard to say that Shinto does not do something. No matter what the practice, you can probably find an example somewhere.