Alas, this is not a Japanese remake of the 1987 body-swap comedy starring Kirk Cameron and Dudley Moore, but a rather uncomfortable drama in which two parents discover their six-year-old son is not actually theirs.
Babies getting accidentally switched in the hospital is the kind of nightmare scenario parents brushed off decades ago because it doesn't happen anymore, but after their son Keita takes a blood test for primary school admission and the fateful mistake is revealed, they're left with wondering what to do with the child they've raised that is biologically a stranger. The Nonomiyas are led by the stern patriarch who has trouble expressing emotion and can't understand how his underachieving (by his standards) son could be his own, and by contrast the Saiki family have a perpetually late father who is happy having fun and living in the back of his shop.
Although there's officially no main character the film is really about Ryota Nonomiya and his interesting approach to fatherhood. When he learns the news he quickly says that "it all makes sense", meaning everything that confused him about his boy must be down to them not sharing DNA. He deems himself a good father because he provides him with a nice home, a good education and some very nifty clothes, but he's distant and stern and wouldn't know encouragement if it punched him in the face. And when he fails to bond with the boy who is his biological son, he soon learns to love his wife and son.
That may sound very Hollywood and twee (FYI, Spielberg is producing an American remake), it's very engrossing, sweet, believable, and one of the best at the fest. In cinemas now.