Kotaro Aoki, Shinko's grandfather, lives with her family in Mitajiri, Yamaguchi Prefecture, during the mid-1950s. A former teacher, he possesses deep knowledge of local history and culture. His captivating stories about the area's ancient past, specifically its existence as the province of Suo with its capital Kokuga a millennium earlier, fuel Shinko's vivid imagination and her belief she can visualize history. He often recounts tales of historical figures like Princess Nagiko Kiyohara, who resided there during the Heian period. Kotaro contextualizes the postwar era, remarking that ten years after the war seem insignificant against a thousand years of history. His narration of Princess Nagiko's loneliness and desire for friendship directly mirrors the experiences of Shinko and her friend Kiiko. He also shares details of daily life in ancient times, such as the significance of mulberry fields for silk production, enriching Shinko's understanding of the landscape. Primarily seen in domestic settings at home interacting with Shinko and her younger sister Mitsuko, Kotaro experiences declining health, culminating in his death during the winter. This event directly impacts the family, leading to their relocation to the city to be closer to Shinko's father's university. His stories and perspective on impermanence leave a lasting influence on Shinko's worldview.