Genzou Senou is the paternal grandfather of Junpei and Kanta Senou, living with them on Shikotan Island. He works as a fisherman, his life anchored to the sea that defines his livelihood and identity. After Japan's defeat in World War II and the Soviet occupation of Shikotan, Genzou and his family are forced to relocate to the stables as Soviets occupy their house.

When the mass evacuation of Japanese residents from Shikotan is ordered on September 25, 1947, Genzou chooses to remain behind. He declares his firm resolve to stay on the island, specifically intending to spend his final moments on his fishing boat – the embodiment of his life's work and bond with the ocean. This decision signifies his refusal to abandon his home and way of life.

Fifty-six years after the evacuation, Junpei and his teacher Sawako return to Shikotan. They discover a gravesite where Genzou is buried alongside his son Tatsuo and grandson Kanta, confirming his death occurred on the island as he intended. The presence of the graves underscores the lasting impact of wartime and post-war events on the family.