Japanese Emperor to Visit Pearl Harbor?

Japan Times reports that the Emperor & Empress of Japan will visit Pearl Harbor on their return from a trip to Canada this summer. According to the article, no prime minister of Japan, let alone the head of state, has been to Pearl Harbor since World War Two. I find that surprising, given the amount of time that has passed, and the close relations between the U.S. and Japan. Even now

the Emperor and Empress will unofficially stop over in Hawaii. They will primarily interact with local Japanese-American groups and visit Pearl Harbor during a break

It sounds like they are trying to keep it as low profile as possible. I'm not exactly sure why. No U.S. president has ever visited Hiroshima either.