After 70 years it still troubled her. In the terror of those moments she had not said thank you. He was long gone by now. Emiko had no idea if he had even survived the aftermath. But he had saved her and she had never said a word to him. "But you were in a state of shock," I said.
"Yes but it bothers me ever since," she replied. We were sitting together in the small sitting room of her daughter's house, among the rice fields about an hour's drive east of Hiroshima.
There was green tea and sweets made from bean paste and the exceptional courtesy known to any who have been guests in a Japanese home. Emiko had gathered all of her photographs and papers, all the speeches she has made against nuclear weapons, and placed them on the table. Now in her 81st year the task of bearing witness has, if anything, become more compelling.
Emiko Yamanaka was 11 years old when the Enola Gay appeared in the skies over Hiroshima. She was on her way from the suburbs to an appointment at an eye clinic when air raid sirens began to wail. The man called out for her to shelter in his garage. All of a sudden there was a flash of light. Then a monstrous roar and the world went black.
Emiko was trapped. She could not move the rubble that covered her. But suddenly she heard a scraping noise and a voice calling. As the bricks were pulled away she saw the man. "It looked as if he was wearing an apron but later I realised it must have been the skin of the front of his body hanging down." He reached his hands in to catch hers and pulled her out. "The skin on his hands came away," she recalled "but it didn't matter because we interlaced our fingers and he got me out anyway." And then he was gone and she was running, faster than she had ever run, to escape the fire. It was following her, a vast malign force always threatening to catch up and consume the fleeing child. Others ran alongside her and she remembers how they clawed at their burning skin in agony.
Through the telling of this story I am drawn to her eyes. They are fixed on me but they are far away, back among the ash-grey acres of the devastated city and the maimed survivors.
After seeing the power of an atomic explosion, the physicist at the heart of the project, J Robert Oppenheimer, quoted from an ancient Hindu text, the Bhagavad Gita: "I am become death, the destroyer of worlds."
The scientists of the Manhattan Project had indeed changed what it meant to be human. They brought to us the capacity for our annihilation. In that single explosion lay the potential of universal destruction.
The bombing of Hiroshima was an act of mass killing deliberately inflicted on a civilian population by democracies fighting a moral war against fascism and militarism. The dead were not collateral damage from a strike intended to destroy only military targets. The purpose was to terrorise and destroy morale, to deliver a shocking blow that would force the surrender of Japan. The bombing of Hiroshima - and Nagasaki a few days later - achieved that aim.
The debates about whether Japan was on the verge of surrender continues with vigorous partisans on both sides. But they often fail to appreciate a crucial point. By that stage in the war, after years of killing and atrocity, allied leaders were brutalised, particularly in their attitudes towards the Japanese, an enemy who ignored the laws of war and whom the Americans regarded with loathing.
Decisions were possible in 1945 that would have been unthinkable at the war's outset. This is the bigger truth of Hiroshima: total war hardens the heart, blunts the senses and makes conscience a captive to the imperative of victory.
Walking by the Motoyasu river which flows through the heart of the city I stopped outside the ruins of the Genbaku dome. There isn't much more than the frame of the old building and a metal staircase twisted by the fierce heat of 70 years ago. A few crows perched there silhouetted against the setting sun. A group of traditional dancers was rehearsing. A monk in bright yellow robes prayed at a stone shrine. Families were enjoying their evening walk.
Hiroshima is both a haunting and beguiling city. I found it a gentler and more welcoming place than all other Japanese cities I've visited over the years.
After a year in which I've spent much time watching the unfinished business of World War II and the Cold War being played out brutally in Ukraine it was a relief to be here among people like Emiko Yamanaka.
In this place the wish for peace has risen out of catastrophe. It is something real and tangible. It speaks with a credibility that the jargon-glutted rhetoric of the modern reconciliation industry cannot achieve. Although Emiko still regrets not saying thank you to the man who saved her life we can thank her and the millions of conflict survivors across the world who have made a choice against bitterness.
Too often we hear only the voices of revenge. Strange as it may seem, leaving Hiroshima I felt better about humanity than I have in a long time.
Fergal Keane is a special correspondent with BBC News