“Past Lives” is a lovely, bittersweet reverie built on a premise that flirts with fantasy.

Are we “fated” to be with who we end up loving and spending our lives with, and if we are, what happens when events conspire to break that fate?

Playwright and screenwriter (“The Wheel of Time”) Celine Song gets a soulful, brittle romance full of longing, regret and loneliness out of that in a story of childhood not-quite-sweethearts whose shared past and Korean heritage tug at them well into adulthood.

Song establishes the sadness that hangs over the story in the opening shot. Three people — played by Greta Lee, Teo Yoo and John Magaro — are observed by strangers across the New York bar who try to figure out what the relationship is between the two Koreans locking eyes and talking with intense interest, and how the scruffy and seemingly miserable “white guy” who is part of this party and whom they “aren’t even talking to” fits its into that.

Are the Koreans siblings?

A flashback to 24 years before settles that. Na Young (Moon Seung-ah) is seen as a “crybaby” 12 year-old, always engaged in academic competition with her friend Hae Sung (Leem Seung-min), and prone to getting upset when she loses.

He clumsily comforts her, but it’s easy to see their connection is deep, even at that age. They kind of want to try a “date,” which might only be a playground playdate, but the “crush” is real as is the attraction .

But she’s about to leave. Her artist mother and filmmaker father are immigrating, and she and her sister have to pick out English-sounding names. Michelle becomes her kid sister’s name, Nora will be hers.

She jokes to Hae Sung and others at school that she can’t stay because “No Nobel prize winners come from Korea,” but that just wounds him.

A long, silent walk home from school sees a quietly-stricken Hae Sung bid a single word “Bye” to his friend as they part ways, with her literally hiking higher and him turning to to take that level side street that signifies his constancy in conflict with her higher aspirations.

As Nora (Lee) and Hae Sung (Yoo) settle into separate futures and diverging destinies, they lose touch. But Nora, pursuing a life as a playwright, acknowledges a certain ennui about her family’s decision to leave, the tug of home and this Korean concept of fate — “In-yun” — that suggests things happen for a reason, that souls fated to be together have had “8,000 earlier encounters that ordain it.

It’s mysterical and traditional and yes, it’s kind of apt that the best online explanation of it comes from the pastor and cult leader Rev. Moon, another Korean immigrant.

Song’s screenplay introduces this idea on three timelines — their childhood separation, their just-after-college years, when social media has made it possible for Hae Sung to “find my friend,” and another 12 years after that, when they finally meet face to face in New York.

The problem with that belated reconnection is that Nora’s now a playwright, bouncing from productions to grants to artist’s retreats, where she met the Jewish novelist-to-be Arthur (Magaro), whom she married.

Song and her finely-tuned performers make the just-after-college-years Skype calls warm and vulnerable. It takes HaeSung a bit to admit that he reached out in search of her because “I missed you.” The bounce that comes to Nora’s step at their renewed contact, the uninhibited smile that Lee wears in the conversations, lets us root for them as a couple.

Yoo’s tentative take on Hae Sung shows us a guy who lives an “ordinary” Korean life — military service, years of nights out drinking with his mates — someone perhaps “stuck” and thus drawn back to this deep childhood connection, but unwilling or unable to grow to make something of it. He learns Mandarin, because “it will help me with my work (in Korean with subtitles),” not English, Nora’s primary language. He urges her to visit Seoul, but isn’t ready to move heaven and Earth to get to New York, where she’s settled.

With her starting her career and him starting his as an “ordinary” engineer, any reunion could be a year or more away. This long distance connection is impractical, and somebody’s going to have to say so.

Song and the cast take the unspoken pain and obvious awkwardness to a whole other level with that third act New York meeting, set in familiar landmarks and striking, under-filmed scenic spots along the river and under the bridges. These scenes ache and truly sell this culture clash/cultural pull romantic premise, far-fetched or not.

Sometimes, the best romances are unconsummated or otherwise incomplete, be they a “Brief Encounter” or trapped in the amber of “The Eternal Sunshine of the Spotless Mind,” a movie that Nora helpfully recommends to Hae Sung. It’s not the “love” that lasts. It’s the longing.

And in filtering that universal emotion through a Korean ex-pat lens, Song has given us THE romance of the summer of 2023.

Rating: PG-13, profanity

Cast: Greta Lee, Teo Yoo, Moon Seung-ah, Leem Seung-min, John Magaro

Credits: Scripted and directed by Celine Song. An A24 release.

Running time: 1:45