in movies about the event life in Hiroshima before the bomb is usually depicted as relatively normal and comfortable. wasn't japan on the verge of famine by the summer of 1945? wouldn't there have already been people in Hiroshima suffering from malnourishment?

While Japan was suffering a great deal from food shortages, they had been on rations for many years and this normalized the small portions they were eating by 1945. Humans tend to acclimatize quickly to situations.

And just because they were facing wartime difficulties doesn't mean that the economy grinds to a halt. If anything, the government would keep people working. People still show up to offices, newspapers still print, factories especially keep churning out goods and supplies.

And people in Hiroshima were malnourished. One of the biggest plot points in Barefoot Gen, the movie you linked, was that Gen's mother suffered from undernourishment throughout the whole movie, both before and after the bomb drops.

It wasn't so dire that people were literally dying but it certainly wasn't 'normal' nor comfortable if compared to peace time.

It was 'relatively normal' because people became used to war, used to rationing, and used to being hungry.

Even if people are faced with hard lives or tough circumstances, if it sticks around long enough, people acclimatize and get used to it. Even people in intense poverty can experience moments of happiness or joy and even terrible poverty can become 'normal' to those who live perpetually in it.

The other key thing is that Japan was on the verge of famine. Literally not having enough food to stave off starvation was about to become a major problem for vast swaths of the country because the bombing had escalated to a point where it was no longer possible to deliver enough food to cities and population centers.

The rural areas were doing little better since so much of their crops were being diverted to the war effort but they at least had the means to produce their own food. City dwellers had to rely on rationing centers and these places were not optimistic about having enough food for the summer, nevermind the winter of 1945.

People dying directly of starvation only occurs in the most dire of circumstances, when someone literally does not consume enough calories to maintain bodily functions. But being consistently malnourished isn't great by comparison either. There's tons of health complications that could lead to death.

Finally, Hiroshima is certainly relatively comfortable compared to, say, all the other cities that are being bombed to smoldering splinters by the intense US air campaign but the kempeitai weren't any nicer in Hiroshima than there were anywhere else. Rations were still tight, work hours for military related jobs long, and the war time administration was not keen on freedom expression or freedom to gather, to put it lightly.