What is the main setting in the novel, Earthlings?

The Akishna mountains are the central location for most of the novel's events. Natsuki's paternal grandparents have a house on the top of the mountain where the whole extended family gathers once a year for the Obon holidays. The house is isolated from the rest of the world and is covered in bugs. There are many rooms and tons of land to wander through. Natsuki and Yuu's relationship flourishes here as children, and it becomes a place of folklore for Natsuki when she grows up and looks back on the idyllic house. Her husband grows so obsessed with her story that he demands to take a vacation there. When Natsuki, Tomoya, and Yuu decide to give up on their human lives and live as aliens, they make the house their base and live within it like creatures from another planet.