"The Place Promised in Our Early Days" is a science fiction anime film set in an alternate post-World War II Japan, divided into two occupied territories: the Union in the north and the United States in the south. The story revolves around three teenagers—Hiroki Fujisawa, Takuya Shirakawa, and Sayuri Sawatari—who share a deep bond and a shared dream. In their middle school years, the trio becomes fascinated with a mysterious, towering structure known as the Ezo Tower, located in the Union-controlled Hokkaido. They vow to build an aircraft together to reach the tower, symbolizing their hopes and aspirations.

Hiroki and Takuya, both skilled in mechanics, work on constructing the aircraft, while Sayuri provides emotional support and encouragement. However, their plans are disrupted when Sayuri suddenly disappears without explanation. Years later, Hiroki and Takuya, now high school students, have grown apart, each dealing with the unresolved loss of their friend. Hiroki becomes withdrawn, while Takuya pursues scientific research. The story takes a dramatic turn when they discover that Sayuri has been in a coma for years, her consciousness trapped in a parallel universe connected to the Ezo Tower. The tower, a product of advanced Union technology, is revealed to be a gateway between dimensions, and its existence threatens to destabilize reality.

As Hiroki and Takuya reunite to rescue Sayuri, they uncover the tower's true purpose and the political tensions surrounding it. The Union seeks to exploit the tower's power, while the United States views it as a threat. The narrative explores themes of memory, loss, and the passage of time, as the characters grapple with their shared past and the uncertain future. The film culminates in a poignant resolution, as Hiroki and Takuya confront the consequences of their actions and the emotional weight of their promise to reach the tower with Sayuri. The story blends personal drama with speculative science fiction, creating a layered narrative that intertwines individual relationships with broader geopolitical and existential questions.