Japanese maestro Kore-eda maintains the intense focus on children's relationships with their parents that distinguished his recent work - Nobody Knows, Still Walking and I Wish - with his new film, which approaches a subject popular with filmmakers: the plight of the families whose babies are switched at birth.
Last year's French-made drama The Other Son added the extra element that the families were Israeli and Palestinian; here, the divide is one of social class.
Workaholic architect Ryota Nonomiya (Fukuyama) drives his 6-year-old son Keita (Ninomiya) with a cold ambition verging on fanaticism. When his compliant wife Midori (Ono) says the local hospital has called them in, Ryota expresses the hope that "nothing messy" will disrupt his regimented life, but he's out of luck.
Keita, it transpires, is the biological son of Yudai and Yukari Saiki (Franky and Maki), home appliance dealers in a dreary outer suburb. The Saikis have been raising the Nonomiyas' real son, Ryusei (Sho-gen).
Kore-eda's screenplay lays all this out in the opening 20 minutes or so: the film's real pleasures lie in watching the way the six characters deal with the situations and how their different responses resolve and shift over time.
More than class is at play. Midori's first reaction is of wonderment and joy, but for Ryota it's much more complex, particularly by contrast with the cheerfully childlike Yudai ("My motto is to put off to tomorrow whatever I can," he announces), who is mostly interested in how much the hospital will cough up in damages.
The two families begin to meet so the boys can get to know each other. Then weekend exchanges up the ante. For the viewer, the tension slowly builds as each boy adjusts to the other family's style and notion of fatherhood and the film becomes an intense, absorbing rumination on the nature of love.
The elements of soap opera in the story make this by far the most approachable of Kore-eda's recent films. Indeed, it feels almost schematic at times, and in particular a stunning plot twist at the mid-point is an uncharacteristic contrivance. But the same mesmerising formal control is on show in the precise and intricate construction and swooningly beautiful visual compositions.
The film may seem to tentatively conclude that love is a practice rather than a genetic imperative, but it is too smart and to alive to complexity of the human spirit to argue that anything is so simple. It's a work of some mastery.
Masaharu Fukuyama, Machiko Ono, Lily Franky, Yoko Maki, Keita Ninomiya, Hwang Sho-gen
PG In Japanese with English subtitles