Junpei Seno is a young Japanese boy residing on Shikotan Island amid the Soviet occupation after World War II. He lives with his younger brother Kanta Seno, their father Tatsuo Seno, and grandfather Genzo Seno. Junpei's daily existence faces profound upheaval as Soviet forces occupy the island, displacing Japanese residents and enforcing new social orders.

Amid language barriers and political strife between their communities, Junpei forms a friendship with Tanya, a Russian girl. This bond becomes central to his occupation experience, embodying the persistence of human connection against cultural divides and historical conflict.

Forced relocations and the dismantling of Shikotan’s Japanese communities directly shape Junpei’s life, challenging his concepts of home and security as geopolitical transformations engulf his family and neighbors.

Junpei’s narrative occurs solely within the film’s depicted occupation period, with no appearances in spin-offs, OVAs, or other official media beyond this timeframe.