The Place Promised in Our Early Days

In an alternate reality where World War II had ended with the Separation of Japan, the northern island of Hokkaidō (or Ezo, as it is called in the anime adaptation) is occupied by the "Union" (referring to the Soviet Union) while the rest of the country is occupied by the United States. In 1974, the Union begins the construction of a strange tower on Hokkaido designed by a scientist named Ekusun Tsukinoe. The anime follows the story of three friends living in Aomori, in northern Japan: two boys, Hiroki Fujisawa and Takuya Shirakawa, both child prodigies; and one girl, Sayuri Sawatari. In 1996, the three are in ninth grade, their last year of middle school, and they are fascinated by the Hokkaido Tower visible across the Tsugaru Strait to the north. Sayuri becomes close friends with the two boys. By 1999, the Cold War is still ongoing with Japan and Hokkaido separated.