National Foundation Day at Meiji-Jingu from the Meiji-Jingu website:
Kigensai is a ritual ceremony commemorating the foundation of Japan. It is said that Emperor Jinmu, the first Emperor of Japan, was enthroned at Kashihara-no-miya in Nara prefecture on this day more than 2600 years ago. During Kigensai, Shinto priests in festive attire offer food and recite prayers, and shrine maidens perform a sacred dance. There will also be a parade of many Mikoshi (portable shrines) on Omotesando towards Meiji Jingu, and the brass band of the “Association of Celebrating the Establishment of Japan” will play in honour of the deities.