Keiji Nakazawa was a 6-year-old schoolboy waiting for summer class on Aug. 6, 1945, in Hiroshima, Japan.

He saw a B-29 bomber fly overhead, followed by the flash of white, blue and orange light. An atomic bomb had been dropped by American airmen. Parts of the school had collapsed behind him, serving to protect him from the blast.

The bomb killed his father, brother and sister. His pregnant mother went into premature labor, and a newborn sister died from radiation sickness just days after the blast.

For Mr. Nakazawa, chronicling the bomb and its aftermath became his life’s work, and he did it as a celebrated comic book artist and writer. His death from lung cancer in Hiroshima on Dec. 19 was reported in Japanese news accounts. He was 73.

In the 1970s, when comic books were still largely thought of as escapism for the young, Mr. Nakazawa’s “Barefoot Gen,” a Japanese manga — a comic book serial — gave its audience an unflinchingly gruesome view of the Hiroshima bombing and a portrait of its survivors struggling for their dignity and humanity amid war.

An image from “Barefoot Gen Vol. 1.” Nakazawa’s work depicted survivors struggling for their dignity and humanity amid war. (Courtesy of Last Gasp Publishing)

“Most treatments in [Japanese] film or literature described the bomb’s effects rather obliquely or genteelly,” said Alan Gleason, one of the series’ translators. “Nakazawa blew all of that away with his brutally graphic pictures of what happened.”

Its readers graphically witnessed the devastation of Hiroshima: rivers filled with charred bodies, skeletal survivors with the skin peeling off, and a black rain that sickens everyone it touches.

“His derivative, cartoony illustrations, full of cute, big-eyed people, seem inappropriate for a story in which mass slaughter is graphically depicted,” wrote comic writer Harvey Pekar in a 1988 Washington Post review. “However, the Gen books can be read with great profit by American adults, many of whom are totally ignorant concerning the domestic situation in Japan during World War II.”

Keiji Nakazawa was born March 14, 1939, in Hiroshima. During World War II, Mr. Nakazawa’s father, a sign painter, had been imprisoned by the Japanese police for speaking out against the military.

At 22, Mr. Nakazawa moved to Tokyo and drew comics in the baseball, samurai and shonen (young boy’s adventure) genres. He was influenced by the work of Osamu Tezuka, a Disney-influenced cartoonist and creator of the robot hero Astro Boy. (Tezuka is often called the father of manga.)

After Mr. Nakazawa’s mother died in 1966, he returned to Hiroshima to collect her ashes. The experience proved a turning point in his career.

“When you’re cremated, there are always some bones left — the skull, backbone, arm and leg bones,” Mr. Nakazawa told the Comics Journal in 2003. “But there were no bones left in my mother’s ashes. . . . I think the radiation must have invaded her bones and weakened them to the point that they just disintegrated at the end. I was appalled.”

Keiji Nakazawa, a Japanese comic book artist who chronicled the Hiroshima bombing and its aftermath, died Dec. 19 at age 73. (Courtesy of Last Gasp Publishing)

“I realized I’d never thought seriously about the bomb, the war and why it happened,” he added. “The more I thought about it, the more obvious it was that the Japanese had not confronted these issues at all. They hadn’t accepted their own responsibility for the war. I decided from then on, I’d write about the bomb and the war, and pin the blame where it belonged.”

The result was a 1966 manga, “Struck by Black Rain,” about a Hiroshima survivor driven by hatred and revenge to kill an American black marketeer. He followed it with “I Saw It” in 1972, a first person account of the bombing.

The following year, “Barefoot Gen” began. The serial follows the main character, a young boy named Gen, during and after the bombing of Hiroshima. It was adapted into live action and animated films in Japan.

Mr. Nakazawa braided his grim story with hope. In one scene, a wealthy family pays Gen to care for one of their relatives, a painter with severely burned hands and radiation sickness. The family is afraid to touch the artist; many survivors believed the sickness was contagious. Gen helps the ostracized man regain his humor and humanity. The book ends with a symbol of renewal: the growth of a new crop of wheat.

Survivors include his wife, Misayo Yamane, whom he married in 1966; a daughter; and two grandchildren.

In 1976, a group of Japanese peace activists came to the United States for a pro-disarmament walk across the United States.

“They were frequently asked about the Hiroshima bombing, and one of them happened to have a copy of “Hadashi no Gen (Barefoot Gen)” in his backpack,” wrote Gleason in the Comics Journal. “The Americans on the walk were astonished that someone had written a comic about nuclear holocaust, and urged their Japanese friends to translate it into English.”

The activists formed Project Gen, a non-profit, volunteer group to translate the work. Eventually, the comic appeared in more than 18 languages including Russian.