"In accordance with the constitution, I vow to fulfill my responsibilities as a symbol to the nation and the people of Japan", said Naruhito, the first emperor born after World War Two.
In her letter to the new Emperor, President Halimah expressed confidence that Japan will continue to prosper amid lasting peace and stability in the new Reiwa era, which she noted fittingly represents the hope that all Japanese people will achieve their aspirations.
From the Seiden State Hall of the Imperial Palace in Tokyo, Naruhito said he will be mindful of the path his father walked as emperor, as well as those taken by the emperors before him - and, likewise, will devote himself to self-improvement.
The Kenji-to-Shokei-no-gi ceremony was held in which the Emperor inherited the Imperial Regalia, or the sacred sword and jewels, and the State Seal and Privy Seal as proof of his accession to the throne, in the Seiden-Matsu-no-Ma state room at the Imperial Palace on Wednesday morning. This vehicle will be the first open-top Century ever constructed by the Japanese auto manufacturer.
Naruhito is to make his first address later in Wednesday's ceremony.
His wife, Empress Masako, a Harvard-educated former diplomat, and their daughter Princess Aiko, 17, were barred from the first ceremony, where only adult male royals participated.
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Japan was in a festive mood celebrating an imperial succession that occurred by retirement rather than by death.
Japan has witnessed a rare handover of its Chrysanthemum Throne by a living emperor.
South Korean President Moon Jae-in also sent salutations, urging Naruhito to remember "pain from the war" and contribute to peace like his father.
Japan's new Empress Masako, in a vehicle, waves as she leaves after attending the imperial ritual at the Imperial Palace, Wednesday, May 1, 2019 in Tokyo.
Surveys show a majority of Japanese people would be in favor of opening the line of succession to girls, but so far, the conservative power elite is standing in the way of change. Only his younger brother, Prince Akishino, 53, and Akishino's 12-year-old son, Prince Hisahito, can now succeed him.
Empress Masako later told reporters that she had accepted Naruhito's proposal after he said: "You might have fears and worries about joining the imperial household".
Though Masako struggled with a stress-related illness described by palace officials as an "adjustment disorder" that kept her largely out of the public eye for years, her public appearances have recently increased. He is the first Japanese monarch to abdicate in more than 200 years, after Emperor Kokaku stepped down in 1817, also for his son. Together, they reached out to the people, especially those who faced handicaps and discrimination, and natural disasters. But he said his father's work will be his guidepost. He attended Oxford University, and became crown prince at the age of 28.