Kumo no Mukou, Yakusoku no Basho

In an alternate history where post-World War II Japan was split between the "Union" in Hokkaido and U.S. control in Honshu, a massive tower was built in the north. From Aomori, across the Tsugaru Strait, three high school students in 1996 vowed to build an aircraft to uncover the tower's secrets. Their plan stalled when one of them, Sayuri Sawatari, fell into a mysterious sleep and was moved to Tokyo for treatment. In 1999, one of the friends, Hiroki Fujisawa, learned that Sayuri remained in a coma and sought help from Takuya Shirakawa to find a way to wake her. Unbeknownst to them, her condition is connected to the tower and larger hidden truths.