Lagrangeville, New York, US - Of all her painful memories from August 6, 1945, what vexes Tomiko Morimoto West the most is how she argued with her mother on that fateful day, trumpeting her role in Japan's war effort and slamming the door on her way out.
It was an eventful morning in Hiroshima. The world's first deployed atomic bomb burst into a 4,000C fireball and flattened the city with a hurricane-like blast, killing thousands instantly and some 140,000 by the end of the year.
West, now 84, recalls a B-29 bomber painting "beautiful" vapour trails above Hiroshima. A "bright, bright light" and the thud of buildings falling. A red flare, looming like a setting sun. A city-wide inferno. Black rain. Charred flesh. Riverbeds full of corpses.
But her overriding memory is how she, as a hot-headed 13-year-old, left her mother on bad terms. At the time, lessons were cancelled and schoolchildren worked in farms and factories or trained to fight off gun-toting US infantrymen with bamboo sticks.
Pumped up with pride and nationalist fervour, her parting words were: "I'm working every day for the government." The door slammed. It was weeks before she found her mother's body, under a crushed building, only identifiable by her clothing.
"When you leave the house you have to hug. You never know, you might not see each other again. Had I known she would have died that day, would I have argued? I never would have done that," West said.
"So, every morning I go pray. I say: 'Mum, I'm sorry. I was not very nice'."
It was a tough lesson, but not the only one that month. Nagasaki's people learned the destructive power of atomic weapons on August 9 and, six days later, Japanese Emperor Hirohito and his generals agreed to surrender, ending World War II.
|Tomiko Morimoto West, 84, with a photograph from her childhood in Hiroshima [James Reinl/Al Jazeera]|
As Japan picked itself out of the rubble, West left the blighted area, studied and got a job with the occupying US forces. She later married a US serviceman. Nowadays, they live in the leafy Hudson Valley, in an all-American home with Japanese cherry blossoms growing at the front.
Like Tomiko and Melvin West, the US and Japan get on fine these days. On Friday, Barack Obama will become the first sitting US president to tour Hiroshima's ground zero, accompanied by Prime Minister Shinzo Abe.
It is a big deal for both countries and revives a thorny question: was the US right to drop apocalyptic bombs on civilians, ostensibly to hasten Japan's surrender and avert a land invasion that would prove costly in US lives?
Critics of that decision say Japan would have surrendered anyway, and that Washington was more interested in showing off its new city-killers to the Soviet Union, pre-empting the coming Cold War and its nuclear arms race.
This puts Obama on the spot. The Nobel Peace Prize laureate is warier of deploying military hardware than many of his predecessors and his decision to lay a wreath at the Hiroshima Peace Memorial suggests remorse over the double doomsday bombings.
White House officials say Obama will not apologise during his remarks. Fifty-six percent of Americans believe the atomic strikes were justified under the circumstances, according to a 2015 Pew Research Center poll.
Disarmament and upgrades
Joseph Gerson, an anti-war activist, said a formal US apology would "upset the debate in the coming presidential election" and give Republicans ammunition against Hillary Clinton, the Democratic frontrunner, who pledges to advance Obama's legacy.
"But, at some point, you have to face history," Gerson, from the American Friends Service Committee, a Quaker group, told Al Jazeera.
Obama's problems do not end there. In April 2009, upon taking office, he delivered a speech in Prague calling for a world without nuclear weapons. Now his presidency is winding down, critics question his efforts on nuclear disarmament.
There have been gains. The New START deal with Russia, ratified in 2010, limited the number of deployed strategic nuclear warheads to 1,550. Obama's Nuclear Security Summit meetings have reduced global stockpiles of weapon-making isotopes.
His 2015 nuclear deal with Iran may have helped avert a nuclear arms race in the Middle East. According to Ben Rhodes, his deputy national security adviser, the administration has "bent the curve in the right direction".
But the gains may be dwarfed by the setbacks.
The US is spending as much as $1 trillion over three decades to modernise its nuclear arms stockpiles. Britain plans to renew its missile-launching submarines. North Korea is now believed to be able to mount a small nuclear warhead on missiles capable of striking neighbours.
Pakistan is deploying small, tactical nuclear weapons that are vulnerable to theft or misuse. Kenneth Luongo, president and founder of the Center for a Secure Nuclear Future, a policy group, described the situation as a "free-for-all in South Asia".
According to Setsuko Thurlow, 84, a Japanese peace activist who was 1.8km from the hypocentre of Hiroshima's blast, Obama is a "decent human being" but he "hasn't done enough to be complimented" on his nuclear disarmament efforts.
Thurlow has her own horror stories from the carnage of 1945. She recalls "thick, black liquid" oozing from sickened relatives as their organs rotted. When dressing, she scoured her skin for "purple spots" of radiation poisoning that were a "sure sign you were to die".
A witness to such terrors, the Toronto resident argues fervently for wholesale nuclear disarmament. Her views are shared by many younger people who endured the Cold War, fearful of nuclear Armageddon. For millennials, however, the threat is less palpable.
|Setsuko Thurlow, 84, speaking about Hiroshima at the Japan Society in New York [Paule Saviano/Al Jazeera]|
The modern nuclear age
"People went back to sleep," Thurlow told Al Jazeera.
Prospects for more deals between the world's top nuclear hoarders - Russia and the US - are bleak, given tensions over Ukraine and Syria. Instead, activists focus on a so-called "humanitarian initiative" to stigmatise nuclear arms via UN talks in Geneva.
Others call for unilateral disarmament - a move that requires more courage than most politicians can stomach.
"The pathway to ultimate nuclear disarmament is filled with hairpin twists, and is a very long road," Luongo said. Belt-tightening in Washington, Moscow and other cash-strapped capitals may hasten arms reductions more quickly than pressure groups, he added.
Army chiefs want weapons they can use on battlefields, not locked up in missile silos. "At some point, decision-making will be driven by dollars, not necessarily by ideology or by arms control calculations," Luongo said.
This would, of course, fall short of the universal scrapping of nuclear weapons demanded by Thurlow, West and other survivors of Little Boy - the oddly innocent codename for the bomb that levelled their city. But it may be the best deal on offer in an unstable world.
West learned her lesson from Hiroshima. Her mother's memory looms large. Instead of rowing with her husband, she turns the other cheek. "I just say: 'OK'. My mother should just see me now," said West, who doesn't have children. "I'm like a different person."
But broader lessons from the calamity have not been learned. Seven decades since mushroom clouds towered over southern Japan, it seems as though humanity will still have enough weapons to wipe out life on the planet for many years to come.
"School systems are failing; media is failing; governments are failing to help young people understand the world they live in," said Thurlow. "They don't know what it means to live in a nuclear age."
Follow James Reinl on Twitter: @ jamesreinl