Japan’s Hirokazu Koreeda has always been an astute observer of all human behavior, but his greatest gift as a filmmaker seems to be his capacity to work with children. Koreeda doesn’t direct them so much as let them react to the universe he has created. The siblings at the center of I Wish, played by real-life brothers Koki and Ohshiro Maeda, often seem oblivious to the cameras around them. Whether painting fantastical landscapes or planning a secret trip, the kids exude an unforced naturalism that’s a rare, marvelous thing. It’s this child’s-eye view of the world that makes the premise of I Wish, which should be intolerably schmaltzy, actually work. Twelve-year-old Koichi (Koki) is living in the south of Kyushu island with his mother. His younger brother Ryunosuke (Ohshiro) is with his father in the north. All Koichi wants is for his family to be reunited. So he hatches a plan: to make a wish on the initial run of the soon-to-be-completed bullet train, which will speed from one end of the island to the other. He has been told that when the northbound and southbound trains pass each other for the first time, the intense energy will be enough to make miracles happen. Although I Wish feels loose, its structure reveals itself after the fact; Koreeda allows his performers to guide the journey, both literally to a town at the midpoint of the region and emotionally to a coming-of-age moment.