The opening scene in “Oh Lucy!” is filmed in cold tones, contains only a single, whispered word of dialogue and seems to be setting the table for a bleak and perhaps violent drama.

Shortly thereafter, the story takes on the trappings of a farcical culture-clash comedy, complete with hilariously ill-fitting wigs and language-barrier jokes.

At other times, it feels like we’re watching a road trip comedy with subtle laughs and revealing insights about certain characters.

Or a complicated romantic triangle.

Or a heartbreaking melodrama about a fractured family.

In the wrong hands, all these mood swings could result in a disjointed, neither-fish-nor-fowl, genre-juggling pileup. But thanks to writer-director Atsuko Hirayanagi and a core cast of outstanding performers, “Oh Lucy!” almost never loses its footing on its way to becoming one of the most entertaining and original films of the year.

Shinobu Terajima’s lead performance as the title character — a lonely, middle-aged, chain-smoking, office drone working in a soul-draining Tokyo office — is authentic and brilliant and filled with small but memorable touches. We understand why Lucy is all but invisible to her co-workers — and yet there’s something intriguing and unsettling but also quite endearing about her.

What’s that? What’s the deal with the name?

Figured you might ask about that.

Her given name is actually Setsuko. She becomes “Lucy” because her beautiful and bubbly but perhaps not altogether trustworthy niece Mika (Shioli Katsunu) convinces her to take English lessons, mostly because it will be of benefit to Mika. (It’s a whole thing. Just go with it.)

Setsuko reluctantly agrees to go along with the plan, which leads her to a tiny classroom located in a seedy joint that looks more like a strip club or an adult massage parlor than a place of education.

There she meets John (Josh Hartnett, doing some of his best work), an effusive American nerd whose aggressively upbeat enthusiasm is so suspicious we expect to see him waving actual red flags about his true intentions.

After enveloping his new pupil in a giant bear hug, John has Setsuko pick a name tag out of a box. The tag reads, “LUCY.” From this point forward, she is LUCY. He also gives her a cheap blonde wig and urges her to get into character as he teaches her phrases such as, “How’s it going!” and “What’s up?”

“I teach American English,” says John, “and when you speak American English, you need to be lazy. Lazy and relaxed.”

To her own surprise, Lucy finds herself enjoying the classes, thanks in no small part to John’s charming ways. We get the distinct (and quite sad) feeling Lucy has rarely enjoyed the attentions of … well, anyone. That Lucy is paying for the English lessons and that John seems like a bit of a hustler doesn’t dampen her enthusiasm for their sessions together.

But then cold reality intervenes when John and Mika suddenly zip off to California without explanation.

Lucy and her judgmental, profoundly joyless sister Ayako (Kaho Minami) get on plane and try to track them down. Is Mika all right? Is John a con artist? Or maybe MIKA is the con artist! What in the blazes is happening?

The California sequences include some predictable scenarios based on language barriers and cultural differences, e.g., Lucy and her sister learning how to say “French fries” in a diner while a millennial waiter smirks at their efforts.

Far more often, however, the story takes unexpected, sometimes startling turns — and our perceptions and sympathies shift. One moment we are absolutely loving Lucy’s newfound boldness and spirit of adventure; the next, we are stunned and saddened by what she’s done.

And yet we never stop hoping she finds some measure of happiness, some kind of deep and abiding connection with another person, some reason to believe her life hasn’t passed her by.

This is director Atsuko Hirayanagi’s feature-length debut (based on her own short film), and it is a most impressive first effort. “Oh Lucy!” is quirky and offbeat and strange and sometimes quite dark — and yet oddly lovable.

★★★1⁄2

Film Movement presents a film directed by Atsuko Hirayanagi and written by Hirayanagi and Boris Frumin. In Japanese and English with English subtitles. No MPAA rating. Running time: 95 minutes. Opens Friday at the Gene Siskel Film Center.