Akihito, 82, and his wife Empress Michiko are in the Philippines to celebrate 60 years of diplomatic ties, while also honouring those who died during Japan's brutal occupation of the Philippines.
"During this war, fierce battles between Japan and the United States took place on Philippine soil, resulting in the loss of many Filipino lives and leaving many Filipinos injured," he said.
"This is something we Japanese must never forget and we intend to keep this engraved in our hearts throughout our visit," he said at a banquet hosted by President Benigno Aquino.
Akihito's visit is the first by a Japanese emperor to the Philippines and comes as the two countries strengthen economic and defence ties, partly to counter China's increasingly assertive actions in disputed regional waters.
Also Read
The official events of his five-day trip began today morning with a red-carpet welcome at the presidential palace hosted by Aquino.
During the Japanese WWII occupation, tens of thousands of soldiers died marching to Japanese concentration camps or during confinement.
An estimated 100,000 Filipinos also died during the month-long campaign to liberate Manila in 1945, which saw aerial bombings and artillery flatten the city.
Akihito has made honouring Japanese and non-Japanese who died in World War II a touchstone of his near three-decade reign -- known as Heisei, or "achieving peace" -- and now in its twilight.