What is family? How do we know the people who come into our lives not by choice or circumstance, but by biological chance? How do we love them? These are the questions that occupy the father of a young child as he faces an impossible decision in Hirokazu Kore-eda’s understated drama “Like Father, Like Son.”

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By all appearances, Ryota Nonomiya (Masaharu Fukuyama) has the model family. He’s a successful architect who puts in long hours at a big Tokyo firm, work that pays off in the form of a sleek high-rise apartment where his wife Midori (Machiko Ono) cooks a late dinner. He wants two eggs with his noodles; she playfully chides him for not considering his health. Behind them, six-year-old Keita (Keita Ninomiya) practices the piano, and Ryota joins him for an impromptu duet.

When a call comes with news that Keita is not the Nonomiyas’ biological son but one of two boys switched at birth, their shock is inevitable. But as Midori sinks slowly into a tide of guilt and grief, Ryota instead feels relief. Though dutiful and reserved, Keita is no prodigy, and Ryota expects his son—like everything else in his life—to be the best. “Now it all makes sense,” he says. 

The mix-up pulls them into the orbit of another couple, shopkeeper Yudai Saiki (Lily Franky) and his wife Yukari (Yoko Maki). They’ve named their son Ryusei (Shogen Hwang) and he’s grown to be a clever, boisterous brother to two younger children. The Saikis are everything Ryota and Midori are not: They arrive late to every meeting at the hospital, driving a tiny van befitting their income and the size of their brood. Their clothes, if a bit worn, are cheerfully mismatched. They laugh and speak their minds with ease, though Yudai seems crudely concerned with how much cash they can squeeze out of the hospital in damages. The ensuing months are a test of everyone’s emotional willpower, as both parents and children become acquainted in order to better make their difficult decision.

At first the two families seem almost comically at odds, but Kore-eda, a former documentary maker and himself the father of a six-year-old, draws them into careful, loving focus. We learn more about each character at a pace that feels deliberate but not forced—a look here, an offhand remark there. We come to know them as we might in real life, their pictures becoming more complete each time we meet them onscreen. Yudai’s preoccupation with money, we find, is a side effect of a driving desire to provide for his family. And Ryota, who at times seems unaffected by the whole ordeal, has a strained history with his own father that colors his perspective.

Even in their most off-putting moments, the characters never completely lose our understanding. It’s no small feat, though Kore-eda owes a lot to his performers, some—like leads Fukuyama and Ono—who have had only sporadic acting careers at best. Fukuyama, in particular, plays Ryota with such convincing depth that audiences unfamiliar with him may find it hard to believe that he’s a beloved Japanese pop singer in real life.

Two families forever changed by a discovery.

The performances are made more effective, too, by their framing. Mikiya Takimoto’s cinematography is rich but not oversaturated, giving the film a sense of vitality even in its quieter moments (of which there are many). A sparsely used piano score highlights the passage of time, but often scenes are allowed room to breathe, with only environmental sounds breaking up the silence. It comes as no surprise that writer-director Kore-eda, who took home the Jury Prize at Cannes for the film, is also credited with its editing.

Still, it’s not the first movie Kore-eda has done triple-duty on, nor is it his first about familial love and obligation (his earlier works “Still Walking” and 2011’s “I Wish” handle those themes as well). But it’s important to note that this film’s original Japanese title translates not to “Like Father, Like Son,” but something closer to “Then he becomes a father.” Midori, Yukari and the children may be rendered here in full, but this is meant to be Ryota’s story of redemption, and Kore-eda strays little from his chosen path.

So what, then, does it mean to be a father? Is it, as Ryota’s own estranged dad explains, an inescapable fate cemented by blood? Or is it a choice to love, as Yudai and others seem to believe? 

An answer may be found in the film’s opening scene, when the Nonomiyas attend an interview for a prestigious elementary school. Keita, wide-eyed and earnest, sits sandwiched between his parents. Facing the family are two school officials—a man and woman dressed in monochrome clothing, mirror images of Ryota and Midori. Between them, however, is a basket full of flowers, bright blossoms leaning gently in the direction of care.