Twelve-year-old Koichi lives with his mother and retired grandparents in Kagoshima, in the southern region of Kyushu, Japan. His younger brother Ryunosuke lives with their father in Hakata, northern Kyushu. The brothers have been separated by their parents' divorce and Koichi's only wish is for his family to be reunited.
When he learns that a new bullet train line will soon open, linking the two towns, Koichi starts to believe that a miracle will take place the moment these new trains first pass each other at top speed. With help from the adults around him, Koichi sets out on a journey with a group of friends, each hoping to witness a miracle that will improve their difficult lives.