Three years after the atomic bombing of Hiroshima, Gen Nakaoka, [Issei Miyazaki], his mother Kimie, [Kae Shimamura], and his adopted brother Ryuta, [Masaki Kouda], scavenge for food and scrap metal to sell on the black market as Hiroshima—and the rest of Japan—struggle to rebuild after World War II. Kimie starts working at a geta factory, while Gen and Ryuta attend school in a ruined building, where they encounter a gang of orphaned children led by Masa, [Kei Nakamura]. The looming presence of the police, embodied by a stern policeman [Hiroshi Ôtake], prompts a tense first clash that sends the brothers scrambling to hide with Masa and his group in their improvised shelter. There, Gen discovers that the orphans survive by pickpocketing in the black market, a harsh reality that deepens the gang’s bond and their shared resolve.
Seeing Masa’s desperation for a better life, Gen and Ryuta choose to stay by his side, entering a world where survival often means bending rules. Gen also forms a quiet friendship with Katsuko, [Kimi Aoyama], a girl among the orphans who bears the scars of the bombing from severe burns. The group grows to include Suekichi, a retired journalist who lost his family in Hiroshima, who comes to live among them and adds a fragile sense of grown-up perspective to their makeshift family. As Gen rallies the orphans to build a new home from wood and salvaged materials found around the city, they stage nighttime raids on a potato field in hopes of securing food, but the farmers catch them and tragedy strikes when Katchin, a member of Masa’s gang, is killed as the kids retreat.
Meanwhile, Gen begins to notice small things that hint at his mother’s decline; he can lift her onto his back for piggyback rides, a sign that her strength is slipping. Doctors reveal the grim truth: the atomic bombing has left Kimie suffering from radiation sickness that will worsen with time. Kimie’s condition worsens, and Gen and Ryuta struggle to cope as the reality of losing her settles in. A doctor, [Junji Nishimura], informs Gen that Kimie has only four months to live, a deadline that steels Gen’s resolve to protect and provide for his younger brother and their growing surrogate family.
Kimie’s illness becomes a crucible that tests their will to stay together. Gen refuses to abandon the vow his father, [Takao Inoue], and his mother instilled in him, choosing to keep the family intact even as the days darken. He and Ryuta step up to help in Kimie’s care, and the siblings continue their tasks—working alongside Masa’s gang and the other orphans—while clinging to the idea of a future beyond scarcity and fear. In the end, Kimie’s death comes while Gen carries her, a heartbreaking moment that crystallizes the cost of survival in a city still marked by the blast.
Gen cremates Kimie and, alongside Ryuta, Masa, Katsuko, and the other orphans, finds a way to honor his parents’ memory while moving forward. The film closes on Gen’s quiet reflection about the lessons his parents taught him—the strength, the tenderness, and the stubborn will to live—woven into the stubborn resilience of the children he has come to lead and protect.
