SEOUL (AFP) - When Moon Jae In heads to Japan on Wednesday (May 9) he will be the first South Korean leader to do so in more than six years, but while the neighbours are both market democracies and US allies facing similar threats, analysts say their relationship is mired in the past.
Moon will attend a trilateral meeting in Tokyo with Japanese and Chinese leaders and hold a separate summit with Prime Minister Shinzo Abe.
Seoul and Tokyo face a common threat from nuclear-armed North Korea, and have both been on the receiving end of Beijing's economic muscle-flexing in recent years.
But despite their shared interests and outlooks, similar difficulties and extensive economic connections, their relations are marred by disputes over history and territory.
Koreans maintain a deep resentment over Japan's colonial rule of the peninsula from 1910 to 1945 and its abuses, including the wartime sex slaves euphemistically known as "comfort women", and say Tokyo has not expressed sufficient remorse.
South Korean national identity is rooted in the struggle for independence from Tokyo, and the history is prominent in education, monuments and culture. Sporting contests between the two are tense affairs, and aside from North Korea, Japan almost always ranks as South Koreans' most disliked country in opinion polls.
For its part Tokyo believes that all such issues were resolved through a treaty to normalise relations in 1965, which included massive economic aid to develop the South, at the time still recovering from the ravages of the Korean War.
Moon himself told Japan's Yomiuri Shimbun newspaper in an interview published Tuesday that he supported "future-oriented cooperation", separate from the issues of history.
But at the same time, he said that "true reconciliation" was not possible unless a "sincere self-reflection and an apology from the bottom of the heart must be conveyed to and received by the victims".
Analysts say the two countries should try to draw a line under the past in favour of "more diplomatic options".
"Korea and Japan both face a lot of shared challenges - North Korea, an unpredictable United States, an aggressive China, and the difficulty of sustaining economic growth," Mintaro Oba, a former US State Department official, told AFP.
"Cooperation between the two governments is both possible and critically important."
Daniel Pinkston, a lecturer in international relations at Alabama's Troy University, added: "It is in the interest (of) both countries to resolve the issues."
Koreans suffered immensely under Japan's colonial rule, Pinkston said, but Seoul now had a shared responsibility to resolve the issue with "some maturity and strength".
"Japan today is not the Japan in the 1930s," he said. "That was then and this is now."
Japan has repeatedly addressed its wartime atrocities, notably the 1993 Kono Statement on the comfort women issue and a landmark apology by prime minister Tomiichi Murayama in 1995.
But contradictory remarks and actions by its own government and politicians have fuelled South Korean distrust of Japan's sincerity, notably the regular appearances by MPs at Tokyo's controversial Yasukuni Shrine, which honours millions of Japanese war dead but also senior convicted war criminals.
The nationalist Abe's own grandfather was arrested as a war crimes suspect but never charged, and a recent poll by Seoul's Asan Institute showed he was South Koreans' least liked leader.
"Tokyo's apologies have been perceived as too little, too late," writes Jennifer Lind of Dartmouth College in her book "Sorry States: Apologies in International Politics".
"Even worse, its politicians repeatedly shock survivors and the global community by denying past atrocities; its history textbooks whitewash its wartime crimes," Lind added.
South Korea and Japan bicker over statues of a comfort woman installed by activists in front of the Japanese embassy in Seoul and elsewhere.
Park Geun Hye, Moon's ousted predecessor, struck a deal in December 2015 with Tokyo under which Seoul promised not to raise the sex slaves issue again and Japan paid 1 billion yen (S$12.3 million) to a foundation dedicated to supporting the victims.
But Tokyo fell short of taking legal responsibility under the agreement, which angered some survivors.
Moon has not torn up the deal, but has called it a "wrongful" solution and said the South would return the money.
That "aftermath" has further complicated efforts to resolve the comfort women issue, said Ha Jong-moon, a professor of Japanese Studies at Hanshin University.
Seoul needed to find a deal with Tokyo that was acceptable to its own public, he said, but added: "The gap is too huge between what South Korea needs and what Japan is willing to do."