Few parents would voluntarily send a son to live in North Korea; Kongsun Yang sent all three of his. In the early 1970s, Yang waved goodbye to his young Osaka-born boys, who later married and started families in Pyongyang. Poor and unhappy, the sons survive today only thanks to support from their parents in Japan.

Banishing teenage sons behind the borders of the one of the world's most repressive countries seems like an act of cruelty, but Yang acted out of love. "He thought he was doing the best for his boys," says daughter Yonghi Yang, the only child to remain behind.

Yang's moving documentary, titled "Dear Pyongyang," shows that her father's fateful decision can only be understood in the context of the extraordinary trials endured by the Korean community in Japan.

Koreans began to arrive in large numbers after Japan's annexation of the Korean Peninsula in 1910. Many arrived voluntarily, but an unknown number -- a head count endlessly fought over in the dreary statistics game played by nationalists -- were brought as slave labor before and during World War II. When the war ended in 1945, about 700,000 of the then 2 million-strong community stayed on rather than return to their homeland, which was then sliding into a war that would kill millions and split the country into two bitterly opposed states.

Japanese Koreans were rendered stateless when the postwar government canceled the citizenship of former colonial subjects in the Alien Registration Ordinance of 1947. Thanks to discrimination, many then found their postwar route to prosperity -- through lifetime employment in large companies -- effectively barred; this is one reason why a disproportionately large number entered the entertainment industry.

Over the years, popular magazines have "outed" many celebrities they have named as zainichi (literally, "foreigners living in Japan," but generally taken to mean Koreans), and speculating on the origins of stars has become a sort of parlor game for bored media-watchers here.

Other zainichi Koreans were "encouraged" to return to their homeland by a mixture of carrot and stick, according to Tessa Morris-Suzuki, professor of history at the Australian National University in Canberra: the promise of a better life in a country billed as a modern Shangri La, versus discrimination and the threat of government-engineered welfare cuts in Japan. As a result, about 93,000 Koreans and their Japanese spouses were repatriated to North Korea between 1959 and the early 1980s.

Says Suzuki: "The Japanese governments involvement [in this process] was deliberately concealed both from the Japanese public and from the zainichi Korean returnees themselves."

When Japan normalized relations with South Korea in 1965, zainichi Koreans had to choose what Kansai Gaidai University anthropologist Jeffrey Hester calls an "administrative category" -- to opt for life as a Kankoku-jin (South Korean) with permanent residency in Japan, or to leave the word Chosen-jin (Korean) on their Alien Registration Card where it had been since 1947, and so become de facto North Koreans.

Most declined South Korean citizenship -- which is ironic in view of the fact that the majority of zainichi originate from the south. However, South Korea was then a poor, U.S.-backed dictatorship, while North Korea, though offering little freedom, at least boasted the rhetoric of a "workers' state." In the early 1970s, families like the Yangs knew little of the horrors being perpetrated in the name of workers in their sons' new home.

Today of course, few but the most hardcore ideologists have any illusions about North Korea. Yang senior, a prominent member of the pro-Pyongyang General Association of Korean Residents in Japan, is one of a dying breed: in his daughter's documentary he can be seen mechanically praising the fruits of the two Kims' half-century rule. But in quieter moments, he admits regret that his sons are still trapped behind the Bamboo Curtain.

The Japanese-born children and grandchildren of first-generation Koreans like Yang now struggle with profound identity issues. Many despise the Kim regime, but remain zainichi out of loyalty to their parents or the desire to protect their cultural heritage. As "stateless" people, they suffer multiple indignities.

"Every time I left Japan I needed special re-entry permission to come back in," says Yonghi Yang. "I was born here, but I had no passport." In the end, she risked the wrath of her father -- to whom the North Korean juche political philosophy was paramount -- by applying for an "enemy" South Korean passport. In so doing, she became one of about 600,000 zainichi to have taken the same route over the years.

Even then, however, problems remain. South Koreans cannot vote in Japan or take top public service jobs -- a prohibition that was the central issue in a recent dispute between public health nurse Hyang Gyun Chong and Tokyo Metropolitan Government. Chong sued TMG after it barred her from promotion on the grounds that she was not Japanese; her brother was one of many who said citizenship should be a prerequisite for public managerial positions.

Not surprisingly, many zainichi are assimilating -- about 10,000 annually according to the Ministry of Internal Affairs and Communications; an option that has grown in popularity amid the backlash from the abductees issue and a gradual relaxation in nationalization rules. Hester believes this is the Japanese government's preferred solution. "They [zainichi] remain the main 'other' in Japan, and the state would prefer to homogenize this undigested other."

For some, especially women who marry Japanese men and disappear into a family register (koseki), it is possible and sometimes desirable to bury the past -- and indeed, to become Japanese citizens it is necessary to take a Japanese name. "We have heard recent cases of schoolchildren finding photographs of their grandparents wearing Korean dress, and being astonished at this background," says Moogwi Kim of the Korean Youth Association in Japan. "Their parents kept it from them."

Can the past be exhumed? "Yes," says investigator Kenji Shimura of Tokyo detective agency Galu. "We get asked by clients to find out the background of people who are suspected of being Koreans. It can be done, although it takes time and we always refuse to take a job like that."

Recently though, while suspicion of the political loyalties of zainichi may have grown in Japan, the prejudice-imposed "stigma" of Korean blood has weakened. Many Koreans wear their ancestry with pride, and even zainichi admit that things have improved -- a little.

"It is not overt discrimination like before, but it lurks in the background," says Yonghi Yang. "We still have some way to go."