In an alternate timeline, post-World War II Japan has been divided and occupied by two rival powers. Hokkaido has been annexed by the "UNION" while Honshu and the other southern islands have come under U.S. occupation. Hiroki, Takuya and Sayuri are two young boys and a girl living in Aomori, the closest province in Honshu to Hokkaido. These three young classmates become fascinated by the gigantic yet mysterious tower that they see across the Tsugaru Strait, promising that one day they will build and fly an aircraft to the tower to unravel its mystery. However, their project is abandoned after the disappearance of Sayuri. Three years later, Hiroki finds out that Sayuri had been in a coma for the past three years, and asks Takuya to help him find a way to revive her. What they don't know yet is that Sayuri's unconsciousness is somehow linked to the secrets of the UNION tower...