The Space Alien takes place in the year following the end of the Occupation (1945–1952), at a time when Japan was struggling to find a firm footing in a brand-new world. Stark reminders of the war remained, such as a concrete storehouse standing alone in a city block that was once home to a neighborhood of wood-frame houses.
During the Korean War, the American military relied heavily on Japanese suppliers for logistical procurement. In a great historical irony, Japan was destroyed by one war and revitalized by the one that followed it. Though the heady growth of the 1960s was a decade away, the economy would begin to markedly improve in 1954.
And yet rice paddies could still be found throughout Setagaya Ward. They wouldn't last for long. Japan was starting over from scratch. Everything was up for grabs—except those principles of truth and justice that will remain the same for every sentient soul in the universe, space aliens included.
Setagaya Ward is located in the southwest corner of Tokyo proper, directly north of the industrial port town of Kawasaki. No longer "sparsely populated," this mostly residential ward has since grown to a population of nine-hundred thousand, the largest in the city.
The Sumida River branches from the Arakawa River along the border between Tokyo and Saitama Prefecture to the north. It flows south and skirts the Imperial Palace before entering Tokyo Bay. Doctor Torai's estate would likely be located in or around Hamarikyu Gardens.
Originally the duck hunting grounds of the Tokugawa shoguns, Hamarikyu Gardens was opened to the public in 1946 and officially designated a site of cultural and historical value in 1952.