The diplomatic novice is filling a key role as Tokyo is embroiled in territorial tussles with China and South Korea and as the United States seeks to increase its involvement in Asia, including through an ambitious free trade pact.
Kennedy, in the most public role of her adult life, will head to Tokyo on Friday days ahead of the 50th anniversary of her father's assassination.
"Growing up in a family dedicated to public service, I saw how people can come together to solve challenges through commitment, communication and cooperation," she said in a brief video message posted on the embassy's website today.
Kennedy said she has long felt personal ties with Japan after accompanying her uncle, the late senator Ted Kennedy, on a trip to Hiroshima when she was 20 years old.
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In 1945, the US dropped atomic bombs on the city and the port of Nagasaki in the final chapter of World War II.
"It left me with a profound desire to work for a better, more peaceful world," Kennedy said of the Hiroshima visit.
Kennedy also addressed a reception at the Japanese embassy in Washington where she pledged to "work as hard as I can to strengthen the alliance."
Secretary of State John Kerry, personally introducing her at the yesterday's evening reception, recalled that he first met Kennedy when she was a girl at the White House as he worked on Ted Kennedy's first Senate campaign in 1962
Kerry, himself a former senator from Massachusetts, recalled that her father had wanted to be the first US president to pay a state visit to Japan. John F Kennedy had been seriously injured by a Japanese destroyer in 1943.