The character known as "Grandfather" functions in two interconnected narrative roles. In the framing story, an elderly man meets a father and daughter awaiting moonrise on a ridge and recounts a personal story from his past, acting as a narrator who connects historical events to the present and channels themes of memory and reconciliation.

Within the inner World War II story, he serves as caregiver to a young Japanese boy. They live near a U.S. prisoner-of-war camp where the grandfather oversees mining operations, marked by a sign bearing the slogan "fokoku kyouhei" (enrich the state, strengthen the military). His daily responsibilities include ensuring the boy's safety amidst wartime tensions.

The grandfather witnesses a pivotal event where American prisoners rescue the boy from drowning. This intervention by perceived enemies becomes the profound act of compassion central to his recounted experience, challenging prejudices and highlighting shared humanity.

His background involves navigating wartime Japan's complexities, holding a position of oversight while developing an unspoken understanding with the prisoners. His care for the boy illustrates familial duty in adversity, though the specifics of their kinship are not detailed.

His character development traces a transformation from a figure immersed in wartime duties to a bearer of a redemptive story. Decades later, sharing this experience with a new generation, he emphasizes reconciliation and the lasting impact of unexpected kindness during a divisive era. His narrative role ensures this moral lesson endures beyond the war's immediate trauma. His significance resides in these interconnected roles as witness, guardian, and storyteller.