Grandfather, Kun’s paternal great-grandfather, served in World War II as a young man, sustaining a leg injury that left him physically impaired. This impairment led to his defeat in a footrace proposed by his future wife—Kun’s great-grandmother—as a condition for marriage. His loss secured their union, ensuring the family’s continuation.

During Kun’s time-travel journeys, Grandfather appears as his younger self in a rural workshop. He mentors Kun through horseback and motorcycle rides, teaching perseverance and balance. These lessons later fuel Kun’s resolve to ride a bicycle without training wheels.

Grandfather’s wartime injury and the race’s outcome emerge as pivotal moments shaping the family’s trajectory. His bond with Kun’s great-grandmother reflects themes of serendipity and generational ties, illustrating how choices and chance ripple across time to influence descendants.

The character’s backstory draws inspiration from the director’s wife’s family history—specifically her great-grandfather’s role as a wartime aircraft engineer injured in combat. This connection roots the narrative in personal and historical authenticity, underscoring resilience and legacy within family bonds.