When the US dropped the bomb on August 6, 1945, Toshiki Fujimori's mother was carrying him, then just a year old, piggyback to the hospital. The impact of the explosion threw them both to the ground, nearly killing him.
"Obviously tensions are growing as North Korea has been pushing ahead with nuclear tests and development," said Fujimori. "Nuclear weapons just are unacceptable for mankind."
But the threat lends a deeper sense of alarm in Hiroshima, where 140,000 died in that first A-bomb attack, which was followed on August 9, 1945, by another that killed more than 70,000 people in Nagasaki.
"This hell is not a thing of the past," Hiroshima Mayor Kazumi Matsui said in his peace declaration at Sunday's ceremony. "As long as nuclear weapons exist and policymakers threaten their use, their horror could leap into our present at any moment. You could find yourself suffering their cruelty."
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Fujimori said that each August 6, his late mother, who also survived, insisted on retelling the story of the attack to children in their neighborhood, saying she had to keep reminding them to help prevent the same mistake from happening again.
Decades later, 73-year-old Fujimori himself is a leader of Hidankyo, a major organization of atomic bomb survivors.
"There is still a lot to do and we must keep working on it."
He said the adoption of the UN nuclear weapons ban, which was boycotted by all nuclear-armed nations, shows that most of the world supports that cause.
Two recent test-firings of Hwasong-14 inter-continental ballistic missiles suggest that major US cities such as Los Angeles and Chicago are within range of North Korean weapons.