The official reason for the emperor's visit, however, is for a tree-planting ceremony, and anti-imperial feeling in Okinawa is running high.
The authorities have responded with a massive security operation which is more reminiscent of a country in the throes of a military coup than of modern Japan. There are police roadblocks throughout Naha, the capital of Okinawa, and people are being stopped and questioned on the streets. Left-wing activists have been detained for questioning.
Okinawa, a sub-tropical island 1,000 miles from Tokyo, was once an independent kingdom with its own language and customs. It was first invaded by Japan in the early 17th century, but was not fully absorbed into Japan until 1879. The Okinawans are ethnically different from the Japanese, and have long been treated as second-class citizens. But Okinawans' bitterest feelings go back to the Second World War, when the Japanese army, fighting in the name of the late emperor, Hirohito, chose to make its last stand on Okinawa against the advancing allies.
The battle for Okinawa lasted from March until August 1945, and cost the lives of more than 100,000 civilians and about the same number of combatants. Many of the civilians died in mass suicides forced on them by Japanese troops who were unwilling to allow the locals - whose loyalty was suspect anyway - to surrender to the invaders. Others died in the intense Allied shelling of the island, which came to be known as the 'typhoon of steel'. The Japanese troops had dug deep bunkers and tunnels, and refused to surrender for weeks despite the overwhelming firepower of the US and British forces.
Because of this the emperor, and the symbols associated with him from the days of the war, including the Rising Sun flag, have always been regarded with deep reservations by the Okinawans. Only last month Shoichi Chibana, a supermarket owner from the north of the island, was given a one-year suspended prison sentence for burning the flag - called the Hinomaru in Japanese - six years ago as a protest against Japanese militarism.
On the first day of his visit, the emperor is due to visit a grave of the war dead, where he is expected to make some sanitised remarks about the war, expressing his 'regret' for 'past sufferings'. Okinawans had repeatedly demanded that his father, Hirohito, come to the island to apologise, but the Imperial Household Agency delayed for too long, and by the time a date was set for a visit in 1988 he had fallen sick. He died soon after.
Akihito has already made several visits to Okinawa as Crown Prince, and in 1975 he and his wife narrowly escaped when a petrol bomb was thrown at them by an extremist. For this reason, 4,700 policemen have been mobilised to provide security during the visit. The Okinawa prefectural government is spending 2bn yen ( pounds 11.4m) on the security surrounding the visit, including the construction of special buildings.
In an attempt to paper over ill feeling, the tree-planting ceremony, to be held on Sunday, is being promoted as a way of 'covering with green' what was devastated by war. But Okinawans feel the timing is late, and no amount of saplings will hide the resentment felt by older islanders towards those who made them suffer.