Ryūta Kondō, orphaned by the atomic bombing of Hiroshima, resorted to stealing rice from a shack in his desperate hunger. Discovered mid-theft by Gen Nakaoka, who initially mistook him for his deceased brother Shinji, Ryūta explained his loss. Gen and his mother Kimie took Ryūta in as part of their household. To support the family and buy food for Gen's malnourished infant sister Tomoko, Ryūta and Gen accepted work caring for Seiji, a hostile, maggot-infested bomb survivor. Though mistreated, they tended Seiji diligently. When they tried to quit, Seiji pleaded with them to stay, confessing their care made him feel human instead of a "rotting corpse." Ryūta returned home with their earnings while Gen stayed overnight. The brothers paid them 100 yen the next day, enabling them to purchase powdered milk for Tomoko. Tragically, they returned to find Tomoko had already died of starvation, deeply affecting Ryūta and the family.

Weeks later, observing Gen's prolonged grief, Ryūta sought to console him. Recalling a belief that wheat wouldn't grow in Hiroshima for 70 years, symbolizing the city's barren future, Ryūta noticed new grass sprouting from the ground during a walk with Gen. He also saw Gen's hair, lost to radiation, regrowing. Ryūta suggested Tomoko had "given" her hair to Gen, implying her enduring presence. This observation renewed Gen's hope and solidified Ryūta's bond with him. Ryūta soon began calling Gen "older brother." Together with Kimie, they honored the deceased by launching a paper boat lantern down a river, symbolizing remembrance and perseverance.

Beyond this immediate aftermath, Ryūta lived with Gen and other orphans in a collective home, supporting each other through hardships. Later, Ryūta robbed gangsters to fund Kimie's medical treatment, leading to his incarceration in a reformatory. After escaping, he rejoined Gen to help publish a novel by Matsukichi, an elderly writer documenting the bomb's atrocities, resulting in brief detention by American authorities. Following Kimie's death, Ryūta found solace in the local baseball team, the Hiroshima Carp. He eventually fled to Tokyo with another orphan, Katsuko, after killing gang members in retaliation for their friend Musubi's death.