Once inside, she quickly developed a fever and lost consciousness for about a week. Her mother did not believe Tanaka would pull through.
When she eventually did open her eyes in the wrecked house, it was the sight of a blue summer sky that greeted her, visible through a gap in the damaged roof.
“It was the same blue sky as the day before the bomb, even though it was a different world to before,” she said. “When I thought about it again later, it made me think that there is still a tomorrow, and that feeling encouraged me.”
She later became a cloisonné enamellist, producing large-panel artworks showing doves and other images associated with peace and the bombing. She says the works are infused with her reflections on the attack so that they may outlive her.
But while her art expresses part of her story, the fact that it appears she was the only one in her junior school class to survive made her reticent to speak openly about what happened until she was 70.
Tanaka’s family had moved to the area where they were exposed only around a week earlier, after being ordered to vacate their central Hiroshima home. At the time, buildings were regularly torn down to prevent fires spreading in the event of a US attack.
Their old house, which was also an inn that often hosted soldiers on their last night before they were shipped off to war, was just 500 metres from what would become ground zero.
Nakajima junior school, which she had attended until she moved, was completely destroyed by the bomb, her former schoolmates effectively removed without trace.
“There’s no record of whether my classmates lived or died, not for these nearly 80 years. It was traumatic, and I never spoke about the bombing,” Tanaka says.
A social taboo around the bombing was also a strong deterrent against speaking out. “To discuss it was seen as bad, and it could affect your chances of marrying. We were made to forget about it,” she said.
Tanaka grew up poor, as many did in Hiroshima after the bomb. After graduating from junior high school, she attended high-school classes at night after work.
She pursued her passion for art, enrolling at Tokyo’s Bunka Fashion College, where her peers included famed designer Kenzo Takada, the founder of the Kenzo clothing brand.
But Tanaka had to abandon her studies for lack of funds, ending up back in Hiroshima as a chauffeur, after learning to drive in Tokyo upon hearing the work was available.
Through the job she was introduced to her husband, and they had two children, with Tanaka becoming a stay-at-home mother. Her mother-in-law was the one who pushed her to try enamel artworks.
“The pieces got bigger and bigger as I started to think of including messages in them … I didn’t know what message to impart at first, but the atomic bombing was a trauma inside me I could not voice.”
Reluctant even to tell her story to her own children, her approach was changed by a 2008 round-the-world trip with Peace Boat, a Japan-based international non-profit organisation that organises cruises to promote peace, human rights and sustainability.
She spoke for the first time on a cruise stop in Venezuela, after a local mayor reacted with dismay upon learning Tanaka had never told her story before.
“He said to me, if I don’t tell it then who will? If I say nothing, the world will return to using nuclear weapons, he said.”
When she did finally speak out, it was on a satellite broadcast from the South American country. Concerned that this might be the first time her children would learn of her past, she wrote them a letter of apology for concealing the truth for so long.
“I had my heart set on continuing to talk about it then. I was 70, more than 60 years had passed without me telling anyone, but I thought my classmates would forgive me and that talking about it might help lay their souls to rest,” she said.
“They all disappeared, and no one knows that they even existed,” Tanaka said, adding she remembers how she and her classmates used to swim in a river and play.
These days, you don’t see so many young people in Japan coming out against nuclear weapons. Someone has to deliver that message
“Talking about it now brings me solace, but before, if I’d been asked to talk, it seemed like a ridiculous thing to say that I had survived and that my art has themes on being exposed to the bomb,” she said.
Her desire to contribute to the anti-nuclear movement remains undiminished, and she has been to more than 80 countries to spread her story. In April she joined her fifth Peace Boat round-the-world cruise voyage, and she continues to receive people at the peace centre she established in her home in 2016.
But while convinced of the importance of survivors telling their stories, Tanaka is less certain on its power to make a difference.
“I think it may have meaning, but whether it is effective, no one knows. Still, the world will get worse if we do nothing and say things can’t change.
“These days, you don’t see so many young people in Japan coming out against nuclear weapons. Someone has to deliver that message,” she said.