Hiroki Fujisawa, Takuya Shirakawa, and Sayuri Sawatari grow up in an alternate postwar Japan where Hokkaido has been annexed by the mysterious Union, and a colossal tower built there is visible from the mainland. Fascinated by the structure, the three friends vow to build a plane and cross the strait to reach it, but before they can, Sayuri falls into a coma and is sent away to Tokyo for treatment. This manga adapts the first two-thirds of the 2004 anime film's plot.