In an alternate history, post-World War II Japan is split into two parts: the alliance of southern Honshu and other islands with the US, and the annexation of northern Hokkaido by the mysterious Union. A metallic tower on Hokkaido, visible from Honshu, remains shrouded in secrecy and impervious to surveillance. In 1996, three teenagers - Hiroki, Takuya, and Sayuri - band together to construct a test aircraft in order to fly over to Hokkaido and unravel the mysterious tower's secrets. However, when Sayuri falls into a deep coma and is transported to Tokyo for medical treatment, their plans come to an abrupt halt. Three years later, the trio remains steadfast in their determination to uncover the truth about the tower, despite their fading aspirations and the adversity they face. Their unyielding bond and commitment to solving the tower's mysteries endure.
