Nobuko, an elementary school girl enduring Hiroshima's harsh summer of 1945 amidst severe food shortages and escalating war, rescues a malnourished kitten from attacking crows. Determined to keep it despite her parents' initial reluctance over scarce resources, she secretly brings the kitten home. Her resolve deepens when she temporarily runs away with the animal, ultimately convincing her family to accept it.

She names the cat Kuro, forming a strong bond and sharing its care with her younger brother Makoto. Together, they scavenge food for Kuro and engage in playful games, the cat becoming a cherished source of laughter and joy for the family during their struggles. Nobuko navigates daily wartime scarcity while ensuring Kuro's well-being, reflecting her persistent and nurturing spirit.

As the war worsens, Kuro repeatedly protects Nobuko from dangers, playing a critical role in her survival. On the morning of August 6, 1945, Kuro exhibits unsettling restlessness, foreshadowing catastrophe. The cat sacrifices itself during the atomic bombing, shielding Nobuko and Makoto and enabling their survival amidst the devastation. This profound loss marks a pivotal moment for Nobuko, underscoring the war's trauma and Kuro's enduring impact.