Hiromi Hasai was being trained to make machine gun bullets when the flash from the atomic bomb that destroyed his city lit up the already bright morning sky. Just 14, he had been pulled from school a week before to help Japan's failing war effort.
Mr. Hasai, now 84, has often talked publicly of his experiences that day, 70 years ago Thursday, when the first of the only two nuclear weapons ever used in war ultimately killed more than 100,000 people. The victims included hundreds of his classmates, who were still at their school near the blast's epicenter. The bullet factory, 10 miles out of town, was paradoxically a haven.
Yet the things that Mr. Hasai saw and felt that day are not recounted by him alone. The person who knows his story best, after Mr. Hasai himself, is Ritsuko Kinoshita, a woman 25 years his junior who is serving as his "denshosha" — the designated transmitter of his memories. It is part of an unusual and highly personal project to preserve and pass on the experiences of atomic bomb survivors, whose numbers are dwindling rapidly.
Mr. Hasai, a retired university physics researcher with a quick and infectious laugh, is still healthy, as are many of the survivors. But the object for Ms. Kinoshita and roughly 50 other volunteer denshosha is to keep telling the stories they have inherited once the witnesses become too frail to do so, to keep alive memories of a traumatic event that has anchored the pacifist sentiment that has pervaded the country ever since.
Today, however, the depth of that sentiment is being severely tested. Prime Minister Shinzo Abe, the first Japanese leader born after the war, is working to loosen restrictions on Japan's military power imposed by the victorious Allies. He is not the first prime minister to seek more freedom of action for Japan, but he is taking the project a step further than his predecessors. Three generations after the conflict, he argues that Japan has earned the right to be a more normal country.
The day after the attack, The Times reported that the bomb dropped on Hiroshima was equal to 20,000 tons of T.N.T. President Truman warned America's enemy of a rain of ruin.
While some of his proposals have generated widespread opposition — notably a bill now before Parliament that would allow the government to dispatch forces abroad to back up the United States military — the war no longer casts the shadow it once did.
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"Even in Hiroshima, memories are fading," said Hidemichi Kawanishi, a history professor at Hiroshima University. There has been much hand-wringing, he said, over a survey released this week by NHK, the national public broadcaster, showing that 30 percent of the city's residents could not name the date the bomb was dropped. (Nationwide, 70 percent could not cite the date.)
It is a trend that many survivors and their denshosha would like to reverse, or at least slow. Ms. Kinoshita has spent years at Mr. Hasai's side as he has addressed groups of students, educators and visitors to Hiroshima's Peace Memorial Museum, near the skeletal monument of its Atomic Bomb Dome.
She can describe how he and his young fellow workers did what they could for the "ghost people" who poured from the city in the hours after the bombing, many with burns so horrific that their flesh fell away when they were touched. She recounts his walk back to town through ruined, corpse-filled streets to find his mother and sister, who miraculously also survived.
"I'm trying to recount his life and his way of thinking as purely as possible," she said.
The number of officially recognized survivors of the nuclear attacks fell by about 6,000 last year, and is now below 200,000. Their average age is over 80.
Professor Kawanishi called the denshosha project, supported by the city-funded museum, an attempt to preserve some of the moral and emotional influences wielded by those with direct experience of the bomb. Although many survivors have left records of their experiences in memoirs and documentaries, which are widely available to the public, they often end up treated as dry historical records.
"The denshosha are essentially putting themselves in the position of that person, so the survivor doesn't permanently disappear," he said. They have an authority that comes with the survivor's blessing to be "heirs" to their stories, he said, and a mandate to keep finding audiences. Survivors often visit schools, for instance, something denshosha could do in their place.
"It's a very interesting experiment in forming and preserving collective memories," Professor Kawanishi said.
So far that experiment is a small one. Ms. Kinoshita, a former tour guide, has known Mr. Hasai for nearly 20 years, since she began giving volunteer tours at the Peace Memorial Museum in her spare time. But the museum did not start recruiting formal denshosha until 2011. So far 13 bomb survivors have agreed to be paired with one or more denshosha, who are required to spend at least three years shadowing and meeting with the survivor before telling their stories in public. One of the survivors has since died.
Ms. Kinoshita and Mr. Hasai say they have faced criticism from survivors not involved in the project, who question whether someone who did not experience the bomb directly can claim to speak for those who did. Others say such a role should be reserved for family members. Some denshosha are children of the survivors, but many are not, and children are not always willing or able to be public representatives of their parents' suffering.
"I've been told more than once that I have no right to tell their stories," Ms. Kinoshita said, before leaving to guide a group of high school students around the Atomic Bomb Dome, armed with Mr. Hasai's memories. When she speaks to groups in the museum's lecture halls, she says, she shows them a PowerPoint presentation based largely on his recollections.
Mr. Hasai said training successors to tell survivors' stories was better than "having them fade into old fairy tales." He said he would like to see the program expanded to allow denshosha to tell the stories of people who died years earlier, but who left records in the years soon after the war that are now in the museum's archives.
"There are all kinds of records, but how many people actually seek them out?" he said. "The freshest memories are stuck in an archive."