Then Crown Prince Naruhito, right, and Crown Princess Masako, second right, are seen before the commencement of Emperor Akihito's "Taiirei-Seiden-no-Gi" abdication ceremony in the "Matsu no Ma" room at the Imperial Palace in Tokyo's Chiyoda Ward, on April 30, 2019.
Naruhito will formally ascend the Chrysanthemum throne on Wednesday.
The treasures, revered symbols of the throne, comprise a sword representing valor, and a jewel representing benevolence, while a mirror - representing wisdom - is kept at Ise Grand Shrine, the holiest Shinto site in Japan.
He is the first Japanese monarch to stand down in more than 200 years.
The main "Ceremony of the Abdication" took place in a state room of the Imperial Palace in front of about 300 people including Prime Minister Shinzo Abe, Crown Prince Naruhito, and Crown Princess Masako.
Naruhito, 59, will ascend the Chrysanthemum throne in a separate ceremony on Wednesday.
With his accession, the new imperial era, named Reiwa (beautiful harmony), will begin.
His father, Hirohito, in whose name Japanese troops fought World War Two, was considered a living deity until after Japan's defeat in 1945, when he renounced his divinity.
Akihito started citing concerns about his age and declining health in August 2016, expressing his wish to abdicate while he was still well and capable.
Akihito has put those principles into practice enthusiastically.
On Tuesday police stepped up security near the imperial palace, a sprawling site in the heart of Tokyo. "I hope the next emperor will, like the Heisei emperor, be close to the people in the same way". He came to speak to people at the same eye level, as was seen in his visits across Japan. He called on the nation to share the hardships of the suffering, and subsequently visited the region for seven consecutive weeks with Empress Michiko in the height of winter.
Emperor Naruhito himself said in a press conference to mark his birthday previous year, "I think.what people expect in official duties will change according to social changes and it would be important to respond to new demands".
With Japan's Imperial House Law lacking a provision on abdication by a reigning emperor and virtually allowing only posthumous succession, the government enacted a one-time law to allow Akihito's abdication.
He has broken new ground in the sensitive role, expressing regret over Japan's wartime actions and gradually modernising the royal family and bringing it closer to the people.
Evocative images of his reign show him and Empress Michiko comforting people affected by natural disasters and reaching out to marginalised groups, including former leprosy patients who were incarcerated in state-run sanatoriums until the mid-1990s.
The Imperial era of Heisei, which was ushered in on January 8, 1989, came to an end, making way to the new era of Reiwa.
Lee's comments are said to indicate Seoul's desire to improve, in the new era, the bilateral relationship, which has deteriorated partly due to a series of rulings by South Korean courts, including the Supreme Court, that ordered Japanese companies to pay compensation to South Koreans requisitioned to work for them during World War II. "This is something that we should never forget", he said.
Akihito will become the emperor emeritus and his wife, Empress Michiko, will become the empress emerita.
While the emperor holds no political power, he serves as a national figurehead. "And yet Akihito wanted nothing to do with chest-thumping "Japan first" nationalism", he said.