What is the annual Shinto harvest festival celebrated by the emperor called?

The annual Shinto harvest festival celebrated by the emperor is Niiname-no-Matsuri, also commonly called Niiname-sai.

During the ritual, the Emperor of Japan gives thanks to the Shinto deities for the previous year’s harvest and prays for abundance in the coming year. The ceremony is held at the Imperial Palace and is also observed at major shrines, including Ise Grand Shrine and Izumo Shrine.

The ritual traditionally followed the last Day of the Rabbit in the eleventh month of Japan’s old lunar calendar. During the Meiji period, its date was fixed as November 23. That date later became Labor Thanksgiving Day, a modern national holiday introduced in 1948.

A frequent source of confusion is the name. Niiname-sai is the common modern term, while Niiname-no-Matsuri is another reading of the same Japanese name. The first celebration after a new emperor’s accession is more specifically called the Daijō-sai, an especially significant enthronement ceremony.