Ryota Nonomiya is a successful businessman driven by money. He learns that his biological son was switched with another child after birth. He must make a life-changing decision and choose his true son or the boy he raised as his own.

It's family first in surprising Japanese melodrama.

In the movies, as in life, family matters, whether we like it or not, so we’re stuck with it. And what matters most in the best pictures about family is the way in which mothers and fathers prepare to do battle for what they claim as their own, to have and to hold.

That thought is the haunting centre of this fine melodrama from esteemed Japanese director Kore-eda Hirokazu (I Wish). Its subject —a story of two boys swapped at birth and the agony that follows when their parents discover that truth—is shattering, but it’s a quiet movie. Like a room full of bad news, the characters here retreat behind their bewilderment into silence, at least, at first, before turning to the law or each other for answers and retribution. The inevitable explosions of disquiet amongst the casualties are dismissed as mere aberrations. Polite entreaties of forgiveness are sought. Reassurances are made. Bad blood lingers. This repression of genuine feeling gives the film an exquisite tension, a terrible emotional claustrophobia. Still, that same energy is the source of the film’s considerable humour. In a way, this is a straight-faced social comedy. It’s a relief when the folks here find that they can laugh at their own foolishness.

Kore-eda has a lot of fun at the expense of parenthood and parenting. He takes for granted that, like sex and politics, it’s a topic that is the surest path to an uncivilised argument between the properly good-natured. His screenplay is a neat scheme that sets up the two families in question as opposing teams. They go head to head on all the essential points: rich vs. poor, cultured vs. earthy, self-consciously aspirational vs. on the lookout for whatever tiny victory one can reasonably wish for.

This has moved some critics to scorn Kore-eda as a stern moralist out to rehearse the ‘nature or nurture’ theme. I’m not sure that’s the point. Besides, Kore-eda’s story dismisses such notions as delusional crap. The little so-called insignificant moments of family life—outings, school presentations, bath time, hurried breakfasts, lingering goodbyes and big-hug welcomes—are the real stakes here.

The look is soft and the music, Bach’s ‘Goldberg Variations’, aids in affecting its frequent mood swings. Kore-eda favours long takes, wide angles, and he only cuts when he has to. The style turns us into keen observers on the lookout for that telling gesture disguised to hide a hurt feeling or secret desire. But it’s not really a ‘realist’ film. Instead, it’s a sort-of lived-in fairytale about an un-reconstructed materialist who learns a tough-love lesson about what it is to be a real dad. In Japan, the movie’s title Then, One Becomes a Father, gives a hint of its true plot.

Ryota (Masaharu Fukuyama) is a moneyed architect and he’s not a bad guy if you can take the ramrod walk, the unenthusiastic good humour, and his resentment of a world that presents so many attractive ways to spend hard-earned cash. On weekends he sneaks into work. “Since you’re here,” his grateful Boss tells him, “I can spend time with my family.”

Kore-eda and co. entrap Ryota in a monochromatic world; his office is a place of straight lines and fluro glare and sober black-and-white suits. Even the family apartment, shared with wife Midori (Machiko Ono) and six-year-old son Keita (Keita Ninomaya), is a boxy five-star high-rise that has all the warmth of a kitchen showroom. It all bespeaks a life of self-satisfied conformity and a stunning lack of imagination.

Like a lot of ambitious young men, Ryota assures Midori that he’s working for the family; especially so their boy has a future. That idea gets shaken up when they discover that their real son, called Ryusei (Hwang Sho-gen), is being raised by a family of battlers, Yudai (Lily Franky) and Yukari (Yoko Maki), who grind out a living in the provinces running a shabby appliance store.

Yudai is a happy dad who likes to get his hands dirty playing with his brood. With a shag of thinning hair and a shuffling walk that looks like he’s left something nasty in his trousers, Yudai faces the world with a smiley shrug. Ryota can’t imagine that his life is anything to envy, let alone competition for his own.

Once the plot kicks in—the parents elect a weekend visit arrangement to ease the boys into their ‘new’ families—Kore-eda carefully maps the uncertain emotional trajectories of each player; Midori and Yukari, indifferent to custom, culture and legality, are aghast at the thought of giving up the child they think of as their own, and reach out to the other, accompanied by the disapproval of their respective spouses. Yudai hides his hurt dignity behind a cheerful disdain for authority—he wants to sue the hospital responsible for the mix-up with the kids—and a sound belief that there’s a benign solution to the dilemma. As for Keita and Ryusei, both well-behaved, well-adjusted lads, it’s all a holiday frolic until it turns out to be real life and then anxiety falls upon them like an abrupt change in season.

But for Kore-eda, the movie is really Ryota’s story; he’s scared of ‘surrendering’ one kid and frightened by the challenge of raising a son who is a stranger. The film’s dominant image is of this handsome recessive man framed off, isolated, alone with his discomfort and pain, looking on at the seeming ease with which everyone else gets on with life’s lessons. His own father isn’t much help: “Blood is everything in humans and horses,” he tells Ryota, who knows the falsity of this wisdom first hand since he was raised by a stepmother.

Kore-eda has a rep as an actor’s director. I hate to reduce a filmmaker’s talent to such glib nods but the performances—all superb, even the thinly written women—are alive to feeling and behaviour that are almost embarrassing in their intimacy. Perhaps the best thing about this gorgeous movie, and I mean that in more than the obvious way, is how it catches you by surprise. Just when you think you’ve nailed a character or a thought, there is something new to grasp. That’s saying more than that it’s not quite predictable. It goes deep and it challenges you to go with it, and it’s rewarding when you do.