The goshintai is the object in the main sanctuary of a jinja that is thought to house the kami. They can take many forms, and as a rule they are concealed at all times. Normally, it is inside the main sanctuary, which is closed up, and even when the doors are opened there are curtains, screens, and quite possibly boxes hiding it from view. There are some goshintai that are never taken out of all the boxes, even when they are moved for repairs to the sanctuary, so even the priests are not entirely sure what they are.
Over the last couple of years, one of the series in the Komorëbi column in Jinja Shinpō has been about the process of rebuilding Kabushima Jinja, in Aomori Prefecture, after a suspicious fire in 2015. The fire completely destroyed the sanctuary buildings, and the goshintai. Thus, it was also necessary to replace the goshintai.
The column in the January 15th issue was about the enshrinement of the kami in the new sanctuary buildings, and included a description of the goshintai. For a manufactured goshintai, there is generally a period of time during which it is just an object, before the kami has “moved in”, so to speak. I’m not sure that there is anything more precise to say about what happens here — as normal, Shinto does not have a generally accepted theological position on this point. The description in the column says that when the goshintai was moved to the main sanctuary it was carried by the priests, and members of the youth association carried a white curtain to surround it and keep it hidden. That rather suggests that the kami moved into the goshintai before the goshintai was moved into the sanctuary, but I am not sure. Sacredness tends to “leak” in Shinto — somewhere a kami has been is still somewhat sacred after they leave, and somewhere they are going to be is already a bit sacred before they arrive.
In any case, the goshintai was not sacred for some period of time after it was completed, and the author of the column saw it and was able to describe it. Kabushima Jinja enshrines Ichikishimahimë Mikoto, one of the three Munakata kami, and is a Benzaiten Jinja. The new goshintai is an image of Eight-Armed Benzaiten, carved from Aomori-grown katsura (Cercidiphyllum japonicum) wood. In her hands, she holds a sword, bow and arrows, and a jewelled rod, among other things, and on her head is Ugajin (or Uka-no-kami), a kami of grain, in the form of a snake with a human head.
If that sounds a lot like an image of a Hindu deity to you, congratulations. Benzaiten is ultimately derived from Saraswati, via Chinese Buddhism. She was identified with Ichikishimahimë early on, and this is one of the syncretic identifications that did not really get ended by the Meiji Revolution. The snake on her head is a standard part of her iconography in Japan, and is probably not supposed to be the same kami as Ukanomitama (“The honourable spirit of Uka”), the grain kami who is often identified as Inari. But, as I have said before, trying to work out whether two kami are “really” the same kami in Shinto is often a fruitless task, and there is not necessarily a correct answer.
Images of the kami are one of the standard forms for goshintai, along with mirrors, swords, and jewels, and images of Benzaiten are common at jinja enshrining that kami, although not necessarily as the goshintai. Despite being quite different from the item that “goshintai” would immediately bring to mind among knowledgeable people, this goshintai is clearly within the Shinto tradition of these jinja.