Japan considers the "rising sun" flag part of its history. But some in the Koreas, China and other Asian countries say the flag is a reminder of Japan's wartime atrocities and is comparable to the Nazi swastika.
That's why the flag has created anger at the Olympics, with some of the host nation's neighbors calling for it to be banned during the Tokyo Games, which start Friday.
There's little prospect that ties between Seoul and Tokyo will improve any time soon. But the flag dispute may ease. Some experts say the COVID-19 restrictions that have banned spectators at most Olympic venues may prevent the disagreement from growing.
Here's a look at the "rising sun" flag and the long-running unease it has caused in Northeast Asia.
There are two rising sun flags associated with Japan, whose very name in Japanese means "the sun's origin."
One is the country's national flag, called "nisshoki," or "hinomaru," which has a red disc on a white background. Few have a problem with this.
The other one also has a red disc, but it is surrounded by 16 rays that extend outward. Called "kyokujitsuki," this one has led to vehement protests from some of Japan's neighbors.
Both flags have been used for centuries. But disputes about the "rising sun" flag date back to the early part of the 20th century. That's when Japan's imperial navy used it as its official flag as the nation colonized the Korean Peninsula and invaded or occupied China and other Asian countries until its World War II defeat in 1945.
It's still Japan's navy flag, used by the Maritime Self-Defense Force and, in a slightly modified version, by the Ground-Self Defense Force since 1954.
These days, ultra-rightists in Japan often use the flag during rallies or on social media.
Japan's government emphasizes that both rising sun flags use the sun as a motif and were used across the country even before the wartime period. Even today, the rising sun with rays flag motif is used in everyday life in Japan, such as to celebrate a big catch by fishermen, childbirth and other festivities, the government says.
"An argument that it is a political statement or a symbol of militarism is completely irrelevant. I believe there is a big misunderstanding," now-Japanese Prime Minister Yoshihide Suga said in 2013, when he served as chief Cabinet secretary.
Japan's neighbors view it differently.
In 2019, South Korea formally requested that the International Olympic Committee ban the flag at the Tokyo Olympics. Seoul said that the flag recalls the "scars and pain" of Asian people who experienced Japan's wartime military aggression, similar to how the swastika "reminds Europeans of the nightmare of World War II."
North Korea's state media, not known for understatement, have accused Japan of trying to turn "the flag of war criminals" into a symbol of peace at the Olympics, saying that is "an intolerable insult to our people and other Asian people."
China is also highly sensitive to perceived slights from the Japanese government, individuals and companies. However, official outrage over history has diminished somewhat, while China's political, economic and cultural rivalry with the United States and European democracies has increased in recent years. When it comes to the flag, it's clearly less sensitive in China than in South Korea.
Use at the Games
On Saturday, when South Korea removed banners at the Olympic athletes' village in Tokyo that the IOC ruled to be provocative, Seoul said it received an IOC promise that the displaying of the "rising sun" flag would also be banned at stadiums and other Olympic venues.
But South Korean media later reported that some activists carried the "rising sun" flag near the athletes' village. Media reports also said Japan's organizing committee ruled the flag isn't banned inside Olympic stadiums.
"It would be inappropriate to ban the flag from naval exchanges because a version is used by the Japanese Maritime Self-Defense Forces," Leif-Eric Easley, a professor at Ewha University in Seoul, said. "However, you would not expect the Tokyo Olympics hosts or Japanese athletes to use the rising sun emblem because it is not the national flag."
Ties between Seoul and Tokyo, both U.S. allies, have suffered for years in part because of disputes over history and trade.
South Korean President Moon Jae-in's office announced Monday that Moon had decided not to visit Japan for the Olympics because the two countries failed to find enough common ground to support a leaders' summit.
Will this get worse?
Some experts say the flag dispute isn't as serious as other points of contention, like Japan's wartime mobilization of Koreans into sexual slavery or forced labor, and won't likely worsen ties.
The flag dispute can still flare, however, if anger among anti-Japan civic groups in the South draw a backlash among the Japanese public, says Lee Myon-woo, deputy head of the private Sejong Institute near Seoul. Lee says South Korea should refrain from a "too excessive, political interpretation" of the flag because there is no sign that Japan is reviving past militarism.
But Bong Youngshik, a research fellow at Yonsei University Institute for North Korean Studies, says the flag wouldn't have become a major issue if Japan had accepted its neighbors' demands for making a more "sincere apology" over its wartime abuse.
The dispute may not have much kindling to fuel it, though, for one key reason: The lack of spectators at nearly all Olympics venues means no one is waving that flag — which means the dispute may die down for the time being.