Shigematsu is an older Japanese man who suffers from radiation sickness after wandering the ruined city of Hiroshima. Unable to work in the fields, he rears carp with his friends to contribute to the community. He transcribes his wartime diaries to secure a marriage prospect for his niece and to reclaim a sense of agency over his traumatic past.

Shigeko is Shigematsu's practical wife who helps him maintain their post-war life. During the war, she carefully stored valuable possessions and supported the family's survival in the ruined city. In the present, she manages household chores without complaint to support her sick husband and niece.

Yasuko is the strong, independent niece of Shigematsu and Shigeko, who act as her guardians. Plagued by rumors that she suffers from radiation sickness due to her proximity to the atomic blast, she struggles to find a husband. She takes pride in her independence but faces the tragic reality of her environment's invisible threats.

Shokichi is a fellow survivor of the atomic bomb who suffers from radiation sickness. Unable to handle the physical labor of farming, he joins Shigematsu in a project to rear carp in a local pond. He hopes the fish will provide food for the village and rebuild his reputation among the working locals.

Asajiro is one of the village's remaining radiation sickness survivors. Facing resentment from busy villagers who view his forced rest as laziness, he agrees to help expand the carp-rearing project as a productive venture to feed the community.

Yoshio is Shigeko's brother and Yasuko's biological father. He walks a great distance to reunite with his family members after the Hiroshima bombing, bringing gifts of toasted rice cakes to celebrate their survival.

Masao is Shigeko's brother who travels alongside Yoshio to locate their family. He recounts his immense relief at discovering his sister and her household survived the atomic blast after hearing a tip from a neighbor.

The manager of the Furuichi fabric factory where Shigematsu works. He shares his rations and alcohol with Shigematsu, explaining the horrifying, long-lasting nature of the new atomic weapon dropped on the city.

Kotaro is Shigematsu's resourceful neighbor in the present-day village of Kobatake. He receives visitors inquiring about Yasuko, acting as an informal community contact regarding her marriage prospects.

Mr. Miyaji is a neighbor of Shigematsu in Hiroshima. Heavily injured by the blast, he stumbles through the ruined city asking for water before parting ways to locate his own destroyed home.

Hashizume is a normally cheerful youth who lives near Shigematsu in Hiroshima. He wanders in shock after surviving the collapse of his school, which crushed many of his classmates.

Tamotsu is an old friend from Shigematsu's village. He helps clear the rubble of Hiroshima and passes along terrifying news about a second bomb dropping on Nagasaki.

Teiko is a childhood friend of Shigematsu. She walks with him through the devastated city, searching for loved ones despite knowing the grim reality of their likely fate.

Gentaro is a young man from the nearby Yamano village. He shows romantic interest in Yasuko, offering a brief moment of hope for her marriage prospects during the summer festivals.

Sato is a police officer Shigematsu meets in the dense smoke and wreckage of Hiroshima. The two men try to understand the sheer scale of the destruction surrounding them.