About one million ethnic Koreans live in Japan, and just over half of them hold Korean nationality. Their community, which long faced discrimination in Japan, now faces a backlash because of North Korea's nuclear test.
Historical roots of conflict
During Japan's colonial rule of the Korean peninsula from 1910 until its Second World War defeat in 1945, hundreds of thousands of Koreans settled in Japan. Some came of their own free will for work or education, others were conscripted into forced labor.
Many returned to their homeland after the war was over when Korea, divided into North and South, gained independence. Much like the peninsula itself, for many of the Koreans who stayed in Japan, their loyalties were split along political lines.
Today, the descendants of those migrants number around a million. Many are naturalized Japanese citizens, but over half a million ethnic Koreans, known in Japanese as the Zainichi, hold citizenship from South Korea or are considered North Koreans.
The North Koreans are represented by the General Association of Korean Residents in Japan - Chongryon in Korean or Chosen Soren in Japanese.
Mun Gwang Woo, the group's international bureau deputy director, says the Chosen Soren supports the political, foreign and economic policies of North Korea. He says South Koreans sold themselves to the United States and are not proud of their Korean nationality.
Chosen Soren members see themselves as allied with the communist government of North Korea - considered one of the most repressive and isolated nations in the world. And many of them support Pyongyang's recent defiance of United Nations sanctions in launching missiles and testing nuclear weapons.
The Chosen Soren has received funding from Pyongyang to run Korean-language schools in Japan. And for decades, members sent money back to North Korea, including to family members. But after Tokyo imposed sanctions on trade with Pyongyang, much of the cash flow has been cut off.
But most of Japan's 600,000 Zainichi hold South Korean passports, though citizenship does not necessarily indicate political affiliation.
They are represented by the group Mindan. Public relations officer Bae Chul Eun says Mindan has tried to maintain good relations with the pro-North Korean Zainichi.
Bae says in the past, the two groups did have civil exchanges, but Chosen Soren turned it into a political issue and reported the meetings to Pyongyang, which halted them.
Mindan members are generally considered to be aligned with democratic and capitalist South Korea, which has endorsed sanctions against Pyongyang.
In addition to their conflicting views on Korean politics, the two groups also differ on what role the Zainichi should play in Japanese society. Neither group wants to relinquish Korean citizenship, in part due to what they say is the harsh treatment and job discrimination many Koreans experienced in Japan in the past.
Bae of Mindan thinks the Zainichi should play a more active part in Japanese politics.
He says Mindan members want the right to vote in Japanese elections, despite not being citizens.
Bae says the Chosen Soren has called Mindan unpatriotic because they think voting would lessen their Korean identity.
Ethnic Koreans - an easy target
In the past many Japanese looked down on ethnic Koreans; they were denied decent jobs and found it hard to get admitted to top schools. But now, thanks to the popularity of South Korean pop culture in Japan, the image of the Zainichi has improved.
However, the Koreans receive unwanted attention anytime North Korea makes the news. Japan has a long-running dispute with Pyongyang over its kidnapping of Japanese citizens in the 1970s and 1980s. And many Japanese feared for their safety when North Korea launched a rocket into the Pacific Ocean and tested a nuclear device in May.
Some Zainichi say during these times their Japanese neighbors treat them coldly, others find notes on their doors telling them to get out of Japan.
Yasumori Fukuoka, a sociologist at Saitama University, has studied the Zainichi community. He says many Japanese take out anger over North Korea's actions on the Zainichi, especially members of the Chosen Soren.
Fukuoka says Japanese extremist groups sometimes attack Zainichi school children and female students get their uniforms slashed with knives.
Negative attention could fall on the Zainichi again soon. North Korea has warned mariners to stay out of parts of the Sea of Japan until July 9th, saying it will conduct military firing exercises. There is considerable speculation in South Korea, Japan and the United States that North Korea may soon test another long-range missile or a nuclear device.