'I stood in front of the house in my summer kimono, looking up. Then the flash came.' Fumiko Kihara, Hiroshima survivor, speaks to Richard Lloyd Parry
In Shoji Kihara's home town, Hiroshima, the most famous landmark is a ghostly grey ruin known to everyone as the Atomic Dome. It was built between 1913 and 1915 as the Industrial Promotion Hall, one of the proudest and most robust Western-style buildings in the city. On 6 August 1945 at 8.15am, the atomic bomb nicknamed "Little Boy" exploded almost directly overhead, incinerating at a stroke its 30 occupants.

Somehow the building, minus its roofs and the copper cladding on its great dome, remained standing, to become a symbol both of Hiroshima's ruin and its survival. Recently, at a cost of Y200m (pounds 1.41m), the Atomic Dome has been renovated and reinforced so that it will stand forever, according to the plaque in front of it, as an eternal embodiment of the city's slogan, "No More Hiroshimas". But Shoji Kihara is not so sure. "Another 50 years from now, I wonder what will remain," he says. "Hiroshima people are forgetting things that they ought to remember. There are so many big new buildings in the city centre. I look at the Atomic Dome, and every year it seems to get smaller and smaller."

Shoji's mother, Fumiko Kihara, is 82, the same age as the Atomic Dome. Like her contemporary, she's a little age-worn and forgetful. Dates and names elude her but she remembers details, and of these she has enough for several lifetimes. Mrs Kihara is a hibakusha, a word coined soon after the bombing. At the time it was a euphemism, but over 50 years it has entered the language as a symbol of suffering, injustice and even pride. It means "explosion-affected person".

Her own parents grew and sold flowers from a little wooden house with a big, colourful garden. They were poor, and after elementary school Fumiko took a job in the local post office, where her life was transformed by the discovery of a remarkable talent. She became a champion manipulator of the soroban, or oriental abacus, the frame of rods and beads still seen in old-fashioned Japanese shops .

She was more than fast, she was a whirlwind and, after representing Hiroshima in regional competitions, she went on to Tokyo and the national abacus championships. She won first prize: Fumiko, the flowerseller's daughter, was now officially the fastest abacus operator in the Empire. A young colleague at the Post Office who was sent to mind her on her visit to the capital reported to his friends that "we have a genius in Hiroshima". When Fumiko was 22, he married her.

Her new family, the Kiharas, was comfortably middle-class but, as the war intensified, life became harder for everyone in Hiroshima. Their first daughter, Kumiko, was born in 1942. At the same time, an elderly postmaster became sick, and Mrs Kihara was given the unprecedented responsibility of taking over his position. Suddenly, she had a husband, a baby, and a post office to look after. "Gomen nasai, gomen nasai," she says, bowing as she explains this, meaning: I'm sorry, I'm sorry - it sounds as if I'm blowing my own trumpet. But plainly she was an unusual young woman: clever, practical and tough.

On top of everything else, the Kiharas frequently had to put up soldiers who were billeted with Hiroshima families on their way to the front. "Our house was on the tramline that led down to the port," she remembers, "and every day I'd stand in front of the house with my daughter and wave the flag at the soldiers climbing on the trams. Conditions were getting worse, and we were always short of food, but we never believed that Japan could lose." It was easier to believe this in Hiroshima than in most cities because, mysteriously, it had suffered almost no conventional bombing; but the longer the war went on, the more inevitable air raids seemed.

On 6 August, Fumiko Kihara got up at dawn, saw to the baby, and started preparing breakfast. Her husband was on his way home from the post office, where he had worked all night. Breakfast was a mixture of rice filled out with a mashed pumpkin, which she had resourcefully pilfered from a neighbour's allotment. There had been one air-raid warning, and then the all-clear sounded; the sky was cloudless and blue. "Then there was the sound of a plane, very loud, so I looked outside. I stood at the front of the house, looking upwards in my summer kimono. And that was when the flash came. I didn't know where I was. I was standing up, but I couldn't get my sense of direction because there was so much dust and it was dark. Most of the house was destroyed, and my child was inside the house.

"I managed to get the pram out of the porch and, as I pulled it out, the child ran into my arms. Her whole body was blood, and her face was all blood. As I hugged her, she died. But then I looked at her face and it wasn't my child. It wasn't Kumiko. It was a friend of hers who had been coming over to play."

Her husband appeared, bleeding but alive, and together they picked their way through the broken timbers of the house. They heard Kumiko inside, crawling and crying. They pulled the rubble off and hauled her out, and pushed the pram away from Kumiko's dead playmate and the darkening, clouded city.

Like all survivors, they assumed that they had suffered a direct hit by a conventional bomb, and it was only as they moved through the city that they realised this attack was different. "It was very hot, and all the people we saw were begging for water. It was horrifying to see them - they were almost naked, because their clothes had been burned, and their skin was burned, and they had no shoes, and looked like ghosts."

Then Fumiko realised that she looked like a ghost, too - the classical lovelorn ghost from a kabuki play: a young woman, in the shreds of a cotton kimono, with hair singed and speckled with ash. For the first time, she noticed that she was burned, on her arms and shoulder and calves, where the kimono had not covered. Fifty years later, Mrs Kihara pulls up her sleeves, and shows the traces of keloid scars: the skin is no longer red, but it is different from an old person's skin, thick and rubbery. The bands and pattern of the summer kimono that she wore 50 years ago are even now faintly visible.

The Kiharas' house was just over a mile from the hypocentre of the bomb. They headed for a schoolyard where they found water, and met a friend whose house was standing and who sheltered them. They believed they were safe, and Fumiko began now to worry about her elderly parents whose neighbourhood was invisible beneath a pall of smoke and dust. Years later, they realised that the air around them was still boiling invisibly with residual radiation, with gamma rays and neutrons.

Mrs Kihara cries only once as she tells her story. "That evening Hiroshima was burning, burning, and you couldn't get near the centre. The next morning the three of us went in to look for father and mother. Their house had two storeys, and it had been completely destroyed, and father and mother had been buried underneath it. We saw only ashes. We found two bodies and the bodies were still burning. We couldn't do anything.

"Everyone was trying to find food and they could barely help themselves, let alone anyone else. There were no doctors and no aid. I can't remember how long we stayed in my neighbour's house. Eventually, they carried me on a cart to my brother-in-law's in the countryside. They tied me to it with ropes, and without them I would have fallen out, I was so weak. My burns were festering and had little maggots inside, and there was no medicine. We mashed potatoes and rubbed them into my arms. We carried father and mother's bones, and buried them in a cemetery in the countryside."

By February 1946, Mrs Kihara was stronger, which was just as well because in that month she gave birth to her second daughter; she had been three months pregnant when the bomb fell. In 1946, a number of babies who had been in the womb on 6 August were born with unnaturally small heads and mental subnormalities, a condition known as microcephaly. "We had heard by then that in the bomb there had been something poisonous," says Mrs Kihara, "and I was afraid that she wouldn't live. She was healthy but food was short, and because I was still very sick, I couldn't give the baby milk. My sister-in-law nursed her, but she never grew very big."

In 1949, Shoji was born. When he was four, his father, who had been intermittently poorly ever since the bomb, died of a sudden brain haemorrhage. Was it caused by the radiation? Nobody knows. Many survivors declined steadily throughout 1945; out of an estimated 130,000 dead, as many as 60,000 survived the initial 24 hours. Others developed unusually high levels of leukaemia and later, other kinds of cancer. But thousands more simply never felt properly well again.

Shoji Kihara doesn't remember his father, but he has no doubt that he would not have died in 1953 if his home had not been struck by the bomb. Shoji grew up in the country town to which his parents had fled from the burned city. He knew that there had been a big bomb and that it had burnt his mother's arms. In his school there were a lot of orphans, whose parents conceived them after the bomb and died later from its effects. There was a widespread belief, for which no evidence has emerged in 50 years of tests and observation, that genetic defects caused by radiation would be visited on the second generation. Every year Shoji goes for a check- up at a special clinic where tests are carried out on his blood, skin and DNA. One day, a school bully teased Shoji about his dead father and scarred mother. "It was then that I began to feel the pride of being a second generation hibakusha, and I began to realise that Hiroshima is a special city."

In his twenties, Shoji became political. By the Seventies, there were dozens of groups in the city, all devoted to the idea of Hiroshima as a nuclear-free capital of peace. But over the years he began to notice something: for all the talk, the Cold War nuclear age was catching up with the city. In the neighbouring port of Kure there is a large naval base, shared by the United States and the euphemistically named Japanese Self Defence Forces. The US Marines have a large barracks in nearby Iwakuni. And all over the earthquake-prone country, nuclear power plants were stealthily being constructed. "Hiroshima sends a message of peace. But when I look around there are many military bases. Japanese minesweepers were sent from here to the Gulf War. The survivors themselves talk only about the experience of the atomic bombing. But the second generation should have a wider view of these things."

Shoji's mother does not attribute her husband's death to the atom bomb. In any case, after his death there was no time to consider such questions. She was alone at the age of 40, with three young children. She started to work again for the Post Office. Without her family and neighbours, she says, she could never have managed.

"I have had a hard life," she says; she is angry, but with whom she is not sure. "I did not do anything bad. I didn't deserve such hard suffering. The US dropped that bomb on ordinary people who committed no crime and had no responsibility for the war. And the Japanese government did nothing to help us. But I don't want their help anyway." She only registered as an official hibakusha years after she was entitled to claim the pension and health benefits.

Today, the fingers that flickered over the abacus are bent in arthritic right angles. She has rheumatism, and a weak heart and bones, and has suffered from tumours in her ear, and cataracts (another common complaint of hibakusha). "Many people envy me now," she says. "I get check-ups and free visits to the doctor. But I would change places with those people any time."

She has two recurring dreams about that day, she says. One is about maggots crawling under her skin. The second is about oleanders. "When I was being carried out on the cart, there were so many oleanders." There is a difficulty translating this word:neither the interpreter nor Shoji Kihara is exactly sure what an oleander looks like. "They used to grow all over the city," Mrs Kihara says. "At this time of year, it was oleanders, oleanders everywhere. Hiroshima has changed. Young people just don't remember the flowers."