When a movie starts with a diagnosis of terminal cancer, what next? The first thing we saw in Akira Kurosawa’s “Ikiru” (1952) was an X-ray of a man’s stomach, with a tumor clearly visible, and Lulu Wang’s new film, “The Farewell,” sets off with similar starkness. An aged woman undergoes a CT scan, and we learn that she has Stage IV lung cancer and three months to live. But here’s the difference. Kurosawa’s hero, a meek civil servant, took stock of his mortality and decided to waste not a drop of the time that remained. Wang’s elderly lady, by contrast, is a merry old soul, already skilled at being alive, and requiring no further encouragement. So nobody tells her that she’s going to die.

She is known as Nai Nai (Zhao Shuzhen), or “Grandma,” and her home is in Changchun, in northeastern China. Meanwhile, her beloved granddaughter Billi (Awkwafina) is in New York, and it’s the distance between them—generational as well as geographical—that the film explores. When Billi was six, a quarter of a century ago, she and her parents, Haiyan (Tzi Ma) and Jian (Diana Lin), moved to America; they still live there, and speak English among themselves. Billi has her own apartment, plus a ring in her nostril and, most recently, a rejection letter for a Guggenheim Fellowship. Great.

What singles Billi out, though, is the aura of loss and loneliness that enfolds her, even before she hears of her grandmother’s illness, and credit for that must go to Awkwafina. Well in advance of her star turn in “Crazy Rich Asians” (2018), she was famed as a rapper, and her music videos, such as “My Vag,” rejoice in a genial bawdy. It’s remarkable to find such swagger—“New York City, bitch, / That’s where I come from, / Not where I moved to,” she declaims, in “NYC Bitche$”—replaced, in “The Farewell,” by the slouch of diffidence and doubt. As Billi, she gives a master class in hangdoggery, complete with bad posture and a lazy gait; it’s as if the land of opportunity has schooled her in disappointment. When her parents fly to China to be with Nai Nai, urging Billi to stay behind, it’s no surprise that she swiftly disobeys, and follows them. Changchun city, bitch, that’s where she goes to, and where most of the film takes place.

For moviegoers, whether they grew up with “The Philadelphia Story” (1940), “The Godfather” (1972), or “Rachel Getting Married” (2008), the gathering of a clan is scarcely untrodden ground. More unusual, in “The Farewell,” is the need for collective deceit. That also arose in Ang Lee’s “The Wedding Banquet” (1993), but there the subterfuge was sexual—the groom was gay, and his parents were in the dark—whereas here the scheming is a matter of life and death. On the surface, everyone has mustered in Changchun to celebrate the nuptials of Billi’s cousin, the befuddled Hao Hao (Han Chen), and his semi-silent Japanese fiancée, Aiko (Aoi Mizuhara). Underneath, however, the revellers are in preëmptive mourning for the matriarch.

In short, this is a two-tone tale, and Wang is careful not to allow one tone to dominate for long. When Nai Nai goes to the hospital, a handsome young medic, who studied in the United Kingdom, discusses her fatal condition with Billi in English; at the same time, Nai Nai, not understanding a word, gives a sly smile and tries to pair them off—“Dr. Song, let me ask you, are you married?” In some ways, despite the valedictory title, “The Farewell” is one big hello, stuffed to the gills with cooking and eating, and crowned with a marriage feast for scores of guests. It echoes to the crack of crab claws and karaoke, but the heaviest noise is that of weeping, as Haiyan’s brother, Haibin (Yongbo Jiang), pledges undying love to the dying Nai Nai.

In Wang’s world, however, even tears get their comeuppance, and it’s only proper that the funniest scene in her film should be set in a cemetery, where the characters come to pray and to offer gifts—fruit, cookies, liquor—at the grave of Nai Nai’s late husband. He was a smoker, so Haiyan lights a cigarette and reverently lays it on the tomb. “He quit!” Nai Nai exclaims. “Ma, let the man smoke, he’s already dead,” Haibin says, adding, “What else can happen?”

Nearby, professional criers, hired by families to lead the chorus of grief, go about their wailing work, and you sense the movie circling lightly around its weighty theme: To whom do we owe our existence, especially as it draws to a close? Whose death is it, anyway?

Some of the dialogue, you could argue, is on the nose, but then the nose isn’t always the worst place to be. Listen to Haibin explaining why Nai Nai need not be aware of her fate—“It’s our duty to carry this emotional burden for her”—and gently chiding Billi and her father. “You guys moved to the West a long time ago. You think one’s life belongs to oneself,” he says. A larger and more daring film (or a Billi more fired up by American liberalism) might have asked how this laudable devotion to the common cause can be used or abused by an overarching state, and you wonder how “The Farewell” would play right now in Hong Kong, where young protesters would like to keep their lives to themselves. As it stands, though, the movie is compact, coolly heartwarming, and gratifyingly uncute. Be warned, though, it also leaves you starving. That crab looked pretty good.

If you think that Billi lacks confidence, try Casey (Jesse Eisenberg), in “The Art of Self-Defense.” He is the protagonist, but there’s not much pro about him. He’s just an agonist. One night, he goes to buy dinner for his dachshund—not unlike Marlowe (Elliott Gould), in “The Long Goodbye” (1973), who wanders out late for cat food, except that Gould is loose-limbed and shielded by cool, whereas Eisenberg is vulnerably taut. It’s no surprise, then, when Casey gets mugged by a gang of nocturnal motorcyclists. A local newscaster reports the assault and describes the victim as “a thirty-five-year-old dog owner.” Such is Casey’s impact on society. No bark and no bite.

Needless to say, he has an office job, though the film, written and directed by Riley Stearns, displays little interest in what Casey does there. His Alpha colleagues treat him like a Delta, and the glummest note is struck when, rather than downloading porn, like your average onanist, he photocopies images of breasts from a magazine and takes the copies home, there to inflame himself in safety. This fellow needs a life, and quick.

He finds it by joining a karate club, run by someone who asks to be addressed as Sensei. (His real name is Leslie. Don’t smirk.) He is well played by Alessandro Nivola, who lets us know that, suave and menacing though Sensei appears, he’s not quite as suave as he believes. It’s a comic performance, clad in the robes of a solemn one. Pupils are shown how to “kick with your fists and punch with your feet”—a lesson that soccer enthusiasts should probably ignore—and told that “everything should be as masculine as possible.” Casey is enraptured. In “Napoleon Dynamite” (2004), another weakling attended a martial-arts demonstration but just sat there, pale and dazed, whereas Casey soon signs up for more, announcing to Sensei, “I want to be what intimidates me.”