Emperor Akihito and Empress Michiko on Wednesday began a three-day tour to Mie Prefecture, their last trip to a local region before the emperor abdicates on April 30.
On Thursday, the couple will visit Ise Shrine, which is dedicated to the ancestral deities of the imperial family, to report the abdication.
The imperial sword and jewel, two of the family's three sacred treasures that play a key role in the succession, are accompanying the emperor on the visit. The other treasure, a mirror, is always kept at a shrine in the sanctuaries of the Imperial Palace in Tokyo.
The two treasures are taken outside only for visits to the Ise Shrine, one of the most important Shinto shrines. The last time the couple went there with the treasures was 2014.
The imperial regalia will be passed on to 59-year-old Crown Prince Naruhito after he ascends to the Chrysanthemum Throne on May 1.
Emperor Akihito and Empress Michiko have actively traveled the country to see people affected by natural disasters and to attend events such as tree-planting ceremonies. The couple finished making visits to all of Japan's 47 prefectures at least twice in November 2017.
The emperor expressed his wish to retire in a rare video message in 2016, citing his concern that he might not be able to fulfill his official duties due to his advanced age. In the following year, the parliament enacted one-off legislation to enable him to abdicate, the first Japanese monarch to do so in around 200 years.
Among the regalia, called "Sanshu no Jingi," the sword and the mirror are currently replicas made for the emperor to keep in his possession. The original items are kept at Atsuta Shrine in Nagoya and Ise Shrine, respectively.
Before World War II, the emperors used to carry the sword and jewel when they stayed outside the Imperial Palace for at least one night. But the custom ceased after the war in light of the principle of separating government and religion in the Constitution as well as security concerns.