Okinagatarashihimë is one of the most widely revered kami in Japan, but very few people even within the country have so much as heard her name. She is one of the three Hachiman kami, and one of the two (with Hondawakë) who are enshrined in almost all Hachiman jinja — the remaining kami is very variable. Okinagatarashihimë is also known as Jingū Kōgō, and Japanese legend, particularly in the Nihonshoki, records her as the wife of one Tennō and the mother of another, and as the main character in the myths that feature her.
She first appears as a shaman, possessed by kami that tell her husband, Chūai Tennō, that he should cross the sea and conquer the Korean peninsula. He goes to the coast, announces that he can’t see any land, and refuses to go. As a result, the kami strike him dead. Okinagatarashihimë then takes on the task of leading the invasion, with the assistance of three kami of the sea. However, she is pregnant, and thus she binds a stone to her belt so that she will not not give birth until she has carried out the will of the kami. She arrives on the Korean peninsula supported by a great wave, and the inhabitants all submit to her without fighting, because they can see that she is supported by the kami. After her return to Japan, she gives birth, but other children of Chūai Tennō want to seize the throne, and plot to kill her son. However, she tricks them, and defeats them, and her son, Hondawakë, becomes Ōjin Tennō. She founds two jinja, called Sumiyoshi Jinja, to enshrine the kami of the sea who supported her, and she herself is enshrined at those jinja now (and at some of the other jinja enshrining those kami, if not all of them). While the legends in the Nihonshoki do not refer to her as Tennō, there are other sources that do, and the Nihonshoki does dedicate an entire volume to her, a privilege normally restricted to Tennō.
The trigger for writing this article was an article in Jinja Shinpō about a Hachiman jinja in Tokyo that held a special matsuri to mark the 1750th anniversary of her death. The dates given in the Nihonshoki make her a figure of the early to mid third century. We know that there are strong mythical elements in the story, because the Korean peninsula was not successfully invaded from the Japanese archipelago (neither Korea nor Japan existed at that time, of course) in the third century. However, in the early third century a female ruler in Japan, Himiko, sent an embassy to Cao Wei, one of the three states in the region that is now China. The records of the visit say that she was a shamanic ruler, which leads a lot of people to think that the stories of Okinagatarashihimë are based, in part, on her activities.
Many Hachiman jinja have o-mamori for safe childbirth, and for the healthy growth of children, and this is because of Okinagatarashihimë’s story. There is a tradition of revering her as a sacred mother, and of revering her and Hondawakë as a mother-child pair. Her story would also make her a good patron kami for working mothers, but that is not something I have seen taken up.
Because she is enshrined in all Hachiman jinja and most, at least, Sumiyoshi jinja, Okinagatarashihimë may well be the most widely enshrined, and honoured, kami in Japan. Despite that, I would expect only specialists to have even heard of her. This reflects a very basic truth about the way Shinto works: practice is vastly more important than doctrine.