In Celine Song’s feature directorial debut “Past Lives,” the past hangs heavily over every moment between childhood friends Nora (Greta Lee) and Hae Sung (Yoo Teo). The pair, who share repeated reunions after two 12-year periods of separation, inexorably dredge up unspoken feelings and fears that neither can let go of despite their best efforts.

Many filmmakers seek to depict the pleasures and pains of nostalgia, especially when it relates to romances that either fizzled out or never began. Song sets her debut apart by gently introducing unexpected and difficult ideas through seemingly small flourishes, giving the core concept real emotional depth.

The film’s editing and sequencing play no small part in the equation, navigating the different timelines in which the movie takes place with solid pacing and subtle but clear character development. While the early sequences of Nora and Hae Sung’s childhood in Korea seem cliché, the precision of these quickly-edited slivers becomes clear as seemingly insignificant memories have wide-reaching effects on the protagonists’ future lives.

Intimate attention to small details in these scenes pays off in later parts of the film, where Nora and Hae Sung finally reunite in person. Visual motifs also accrue meaning, giving innocuous entities like pools of water, sculptures and even certain colors an added poignancy because of their relationship to the concerns of the past that endlessly interrupt the present.

The past’s influence on every character’s understanding of themselves is subtly drawn yet designed to tug on viewers’ heartstrings, and the film succeeds in large part due to the incredible cast. The actors’ performances skillfully pack complex, contradictory emotions into almost every frame. Even Nora’s husband Arthur (John Magaro), who enters the film at around the 30-minute mark, finds a wealth of humanity in his role as a man who feels he’s wandered into somebody else’s love story.

“Past Lives” leaves much to applaud regarding storytelling and subtle delivery of themes. It’s easy to overlook how well-judged even the most minor musical cues are, with a score that nicely harnesses twinkling keys and soft ambient tones to enhance scenes without overpowering them.

Audiences seeking a movie that takes a mature look at themes of identity’s relationship to the environment, the immigrant experience and people’s responses to their understandings of one another being challenged will find that “Past Lives” delivers on all fronts. Viewer beware: tissues may be a worthwhile investment before watching this picture.

4 pools of water out of 5