The combined Issue 275/276 of the Journal of Shinto Studies (神道宗教) included an article by Itō Yūsukë (伊東裕介) on the requests made by the Tennō of the kami in the Heian period, around a thousand years ago. The article concentrates on Tennō from the late ninth and early tenth centuries, when the system was just getting established.
The article focuses on two questions. The first concerns the name used for this practice, which in later years was “gogan” (御願). Itō confirmed that, in the time period he was looking at, this term was only used in a Buddhist context, and its use within Shinto started about a century later. This suggests that the practice itself may also have been modelled on Buddhist practices.
The other question is how this practice fitted in to the rituals for the kami that were performed by or on behalf of the Tennō. The laws defined a set of these, performed on the Tennō’s behalf by the bureaucracy, but the rites that Itō is looking at were additional to the legally defined set. Further, these petitionary rites involved sending emissaries to venerate kami other than Amaterasu Ōmikami — in other words, kami that were not the Tennō’s ujigami.
Itō’s conclusion is that there do not seem to have been clear standards here. They were connected to the Tennō’s personal requests, but they were also supported by the nobles who ran the bureaucracy, particularly the Fujiwara clan. A particularly clear bit of evidence for that is the “personal” requests made immediately after his accession by Suzaku Tennō, who was eight years old at the time, and thus probably not actually behind the decision. This also helps to explain why the requests were sent to various kami — this was an established practice for the Fujiwara. (Some of the requests were sent to the Fujiwara ujigami, to whom the Tennō had a connection on his mother’s side, but not all.)
The range of requests was also very broad. It was standard to send emissaries soon after a Tennō’s accession, and this became formalised by the eleventh century. There were also far more requests than normal during a period in the tenth century when there were rebellions in two parts of the country at almost the same time. However, there were also other requests, and it seems that the Tennō could ask anything.
In these requests, the distinction between the individual who happened to be the Tennō, and the Tennō as the ruler of the country, seems to have been unclear. They were personal requests, which would tie them to the individual, but they could be organised by ministers on the Tennō’s behalf, which links them to the state.
These days, the Tennō’s relationship to the kami seems to be almost completely formalised. When the Tennō officially visits a prefecture outside Tokyo, he makes offerings to the jinja in that prefecture that received offerings from the state in the pre-war period. These are, of course, legally entirely personal, because the government cannot make offerings at jinja, but they trace back to the official government offerings a thousand years ago more than to the personal offerings. There are also jinja to which the Tennō sends emissaries every year, or at longer intervals, and these trace back to the personal offerings — but this custom was established by the government in the Meiji period, based on the later formalisation of this system. On the other hand, the previous Tennō occasionally visited particular jinja entirely on his own initiative.
The relationship between the Tennō and the kami has, it seems, always been somewhat unclear.