Tatsuo Senô, father of Junpei and Kanta Senô, lives with his sons and his own father, Genzō Senô, on Shikotan Island. He spearheads the village firefighting force. After Japan's surrender in World War II and the Soviet occupation of Shikotan, Tatsuo secretly aids the local Japanese population. With help from the school teacher Sawako, he accesses and distributes food from the Dawn Corps' emergency stores to villagers in need.

This resistance results in his arrest by Soviet forces when his brother-in-law, Hideo, discovers the food cache and tries to smuggle supplies away. Tatsuo is apprehended at the storage cave and transported to a Russian prison camp. On September 25, 1947, during the forced relocation of Shikotan's Japanese residents to internment camps, Tatsuo remains imprisoned. His family, including Junpei and Kanta, is moved to an internment camp at Maoka in western Karafuto.

Hideo later discovers Tatsuo is alive in a nearby camp. This prompts Junpei and Kanta, accompanied by Sawako, to journey to find him. They reach his camp, sharing a final, charged farewell where Tatsuo vows to return to his family no matter what. This meeting is their last.

Tatsuo never reunites with his family. Decades later, visiting Shikotan 56 years after the events, Junpei and Sawako pay respects at graves dedicated to Tatsuo and Kanta. The gravesite confirms Tatsuo's ultimate fate as deceased, though the specific circumstances and timing of his death remain unspecified within the narrative.