TOKYO — Every time Jiro Oshima wants to see his siblings, he must travel to North Korea.

Mr. Oshima, 79, a retired schoolteacher in Japan, takes a flight to Beijing, then another to Pyongyang, carrying small gifts like candy and underwear, and items that his siblings can sell: baby clothes, medicine, shoes.

He has made the journey more than a dozen times since the 1960s, when his parents and siblings moved to the Communist nation as part of a repatriation program that the world has largely forgotten.

Now, as President Trump and North Korea’s leader, Kim Jong-un, prepare for a second summit meeting, to be held in Vietnam this week, there is nervous anticipation that a political thaw could ease the North out of its long isolation. Perhaps nowhere is that hope stronger than among ethnic Koreans like Mr. Oshima in Japan — a community that embraced North Korea as the rest of the world cut it off.

An estimated 322,000 ethnic Koreans in Japan are members of families that arrived during Tokyo’s 35-year colonial occupation of Korea. Known as the Zainichi, most trace their roots to what is now South Korea.