In this alternate world, Japan is divided after World War II: Hokkaido, renamed "Ezo, " belongs to "the Union; " the rest of the archipelago is an American dependency. Ezo is dominated by the Union Tower, a seemingly topless needle. Middle school students Hiroki and Takuya dream of visiting the Tower, and start building an airplane. They're joined by Sayuri, who nurtures a crush on Hiroki. As the characters move into high school, Sayuri falls into a coma. Hiroki and Takuya learn that her dreams are linked to the Tower and to experiments in contacting parallel universes.