Police officers stand guard in front of the Imperial Palace, on the day Emperor Akihito abdicates in a royal ceremony, in Tokyo, Japan, April 30, 2019. REUTERS/Kim Kyung-Hoon 

Japan's Emperor Akihito walks for a ritual called Taiirei-Tojitsu-Kashikodokoro-Omae-no-gi, a ceremony for the Emperor to report the conduct of the abdication ceremony, at the Imperial Palace in Tokyo, Japan April 30, 2019, in this photo released by Imperial Household Agency of Japan. Imperial Household Agency of Japan/Handout via Reuters ATTENTION EDITORS - THIS PICTURE WAS PROVIDED BY A THIRD PARTY. 

Japan's Princess Aiko arrives at the Imperial Palace, where Emperor Akihito will abdicate in a royal ceremony, in Tokyo, Japan, April 30, 2019. REUTERS/Kim Kyung-Hoon 

Japan's Prince Hisahito arrives at the Imperial Palace, where Emperor Akihito will abdicate in a royal ceremony, in Tokyo, Japan, April 30, 2019. REUTERS/Kim Kyung-Hoon 

Japan's Crown Prince Naruhito and Crown Princess Masako arrive at the Imperial Palace, where Emperor Akihito will abdicate in a royal ceremony, in Tokyo, Japan, April 30, 2019. REUTERS/Kim Kyung-Hoon 

Japan's Crown Princess Masako waves as she arrives at the Imperial Palace, where Emperor Akihito will abdicate in a royal ceremony, in Tokyo, Japan, April 30, 2019. REUTERS/Kim Kyung-Hoon 

Chinese tourists take photos in front of the Imperial Palace in Tokyo, Japan, April 30, 2019. REUTERS/Kim Kyung-Hoon 

Korean resident in Japan, Kim Fuzan in traditional pilgrim attire walks along the Imperial Palace as he wishes a successful abdication for the emperor in Tokyo, Japan, April 29, 2019. REUTERS/Kim Kyung-hoon