For decades, Hiroyasu Tagawa had no intention of breaking his silence about his terrible experience as a child of the U.S. atomic bombing of his hometown.

He didn't want to relive the memories of Aug. 9, 1945 and its aftermath and even avoided uttering the words "atomic bomb."

A sixth-grader at the time, Tagawa spent years regretting taking his father to a temporary first aid station where his feet were amputated with a carpenter's saw on the day of Japan's surrender in World War II.

His father had suffered severe burns to his feet when chemicals spilled in a factory as a result of the blast.

"It hurts!" This was the first expression of raw emotion by a man who until the amputation had endured the pain wordlessly, and it continued to haunt Tagawa in the following years. His father died a few days later.

"Had I done my best for him?" Tagawa recalled having repeatedly asked himself.

"I wondered if I had done wrong by taking him over there. Had I not brought him to have the surgery, maybe he would've lived for a longer time. Such regrets felt like thorns in my heart."

Tagawa's reunion at the age of 77 with the nurse who was present during his father's amputation surgery gradually led to him breaking his silence about the bitter experience.

The nurse explained his father let out words of pain when a spinal anesthetic injection was administered and that the doctor had to use the saw because no other surgical tools were available.

"Thanks to finally meeting her, at last I began to forgive myself and free my heart from all these troubling regrets."

Tagawa's story has joined the collected accounts of other survivors of the atomic bombing of Nagasaki, in a form both traditional and modern.

His tale is told in a "kamishibai" picture story show -- a form of storytelling popular with children before the emergence of television -- that has been digitalized and uploaded to YouTube to reach a wider audience in the age of the internet and smartphones.

Titled "That Day, August 9th, and the Future," the roughly 20-minute clip consists of 28 picture slides, each drawn by local students at Mikawa junior high school. It is available in English as well as Japanese so that its message can resonate abroad as well as at home.

The students took about four months to finish off the original picture story show, which depicts how Tagawa survived the atomic bombing and the mental impact on him thereafter, according to a Nagasaki city official involved in the project.

This year marks the 73rd anniversary of the 1945 atomic bombings of Hiroshima on Aug. 6 and Nagasaki three days later. The aging of "hibakusha," as survivors are known in Japanese, has made it ever more urgent to record untold stories and pass them down to future generations.

Educating youngsters about the nature of the atomic bombing in Nagasaki, which had killed nearly 74,000 by the end of 1945, and raising awareness at home and abroad are taking on greater importance, people involved say.

"What is the best way for hibakusha stories to get passed down? This is the most difficult part," said Ayaka Mine, a city official in charge of the project.

"It's true that some hibakusha prefer photos to expose the truth," Mine said. "But the pictures drawn by students are soft and not too sophisticated at times, which helps stimulate the imagination."

Tagawa also likes the students' artworks, she added.

Nagasaki has been trying to deepen understanding of the atomic bombing, calling for the abolition of nuclear weapons.

The city government, for instance, translates its mayor's peace declaration on Aug. 9 into 10 languages, with this year's declaration coming at a time when North Korea's pledge to denuclearize has grabbed global attention.

For visitors, the Nagasaki Atomic Bomb Museum has made its leaflets available in French and Russian since last year, in addition to English, Korean and Chinese. Roughly 20 percent of all leaflets given out to visitors in fiscal 2017 through March were in those five languages.

Located near the hypocenter, the museum is one of the city's most famous spots for visitors from the rest of Japan and abroad and introduces Nagasaki's history before and after the bombing.

Local residents say Nagasaki has seen an increase in the number of foreign tourists in recent years, particularly from Asian neighbors such as China, South Korea and Taiwan.

Lin Yihsuan from Taiwan decided to visit Nagasaki during her recent trip to the Kyushu region in southwestern Japan.

"It's now a peaceful place," Lin, in her late 30s, said as she visited the hypocenter area. She studied Japanese history and the atomic bombing of Nagasaki when she was a junior high school student and wanted to visit at least once.

"We need to pass it down because it was an important event (in history)," Lin said.

For Lin, seeing was believing.

But with the easily accessible digital kamishibai, an actual visit may not be the only way to learn Nagasaki's history.

"Our digital kamishibai does not target a specific audience," said Mine, the Nagasaki city official. But having an English version "raises the chances of reaching more people."

That would also reinforce Tagawa's belief in the power of one person making a difference in the life of another.