Well-wishers are gathering along a central Tokyo street hours before Emperor Naruhito and Empress Masako are expected to greet them from a royal motorcade under tight security.
Police have set up 40 security checkpoints. Selfie sticks, bottles and banners and even shouting are not allowed inside the restricted zone.
Emperor Naruhito succeeded his father Akihito on May 1 following his abdication, and formally ascended the Chrysanthemum Throne in a palace ceremony last month.
Emperor Naruhito and Masako will greet the people Sunday afternoon from a Toyota convertible during their half-hour motorcade on the 4.6-km (3-mile) route from the palace to the Akasaka imperial residence.
The parade was postponed from the original October date due to the recent typhoon that left more than 90 dead.