Kisaburō Nakane occupies the position of the third son and middle child within the Nakane family, flanked by older brothers Tadayoshi and Takejiro and younger sister Kayoko. He shares a notably close relationship with Kayoko, frequently exhibiting protective instincts toward her. When neighborhood boys bully Kayoko, forcing her through a puddle to ruin her dress, Kisaburō intervenes decisively. He drives the bullies away, brandishing a stick and implying physical force, gaining a reputation for his readiness to defend his sister.

Although Kisaburō occasionally joins his older brothers in roughhousing directed at Kayoko, he generally avoids being the primary instigator. He and Kayoko often find themselves in embarrassing or accident-prone situations within the family, resulting in a shared "Butt-Monkey" status. Actions like Kisaburō attempting to run away after defending Kayoko required her intervention with their parents, reinforcing their mutual support and deepening their sibling bond.

Surviving the Tokyo firebombing raids by climbing through an open window to find shelter while the rest of their immediate family perished marked a traumatic turning point. Physically unharmed but emotionally shattered, Kisaburō journeyed alone to Numazu to find Kayoko, evacuated earlier to their aunt's home. Upon arrival, visibly distressed and reflecting deep psychological trauma, he delivered the devastating news of their family's deaths. His survival and subsequent reunion with Kayoko underscored his resilience amidst profound loss.

Following this reunion, Kisaburō and Kayoko returned together to the ruins of Tokyo. Their shared grief and survival instinct forged them into a dedicated brother-sister team, relying solely on each other for emotional and practical support in the war's aftermath. Final scenes depict them conversing amidst the devastation, confirming their continued partnership as they navigated the challenges of the destroyed city and an uncertain future.