There are not many films with a brother-sister relationship at their center. This is because our society does not value this relationship particularly highly.

When sisters who were close to each other fall away, it’s seen as sad. When it happens to a sister and brother, it’s more like life just getting in the way, and what can you do?

But sometimes, a brother and sister are all they’ve got. This is the premise of three very good movies: “You Can Count on Me” and “The Savages,” both with Laura Linney, and now, “Ms. Purple,” an obviously low-budget but highly moving film set in Los Angeles’ Koreatown.

These movies serve as important reminders to call your brother, or sister. But since they come out only once every several years, it doesn’t feel like a burden.

Directed and co-written by Justin Chon (2017’s “Gook”), “Ms. Purple” focuses on the frayed relationship between siblings Kasie (Tiffany Chu, who grew up in San Jose) and Carey (Teddy Lee). Although Kasie and Carey are each other’s only sibling, they are estranged at film’s start.

Their mother abandoned the family years ago, and their father (James Kang) lies comatose in a hospital bed set up in the family’s tiny home. To pay for care, Kasie works as a hostess at a karaoke bar, enduring the grabby attentions of drunken businessmen.

She calls Carey, who left home at 15 after a physical fight with their father, out of desperation when her home health aide quits. When Carey arrives in a dirty T-shirt after what appears to be a long spell down on his luck, Chu delineates the fake smile Kasie flashes at the karaoke bar from the genuine one she shows her brother.

凯利和他姐姐的坚持their father remain at home instead of going into hospice, seemingly out of guilt at not having been around to help. But it is also because he respects and loves her, the siblings’ affection expressed not in words but in the lived-in ease the actors bring to their interactions.

也许成长的结果与一个贫穷的唱歌le dad who seemed overly emotional (Kang is very good in flashback scenes) about the family’s circumstances, Carey and Kasie have suppressed most outward signs of emotion. But Chu and Lee show the emotion roiling beneath the surface when the siblings discuss what Kasie does for a living.

Chu gives her character a touch of defiance as she asks Carey if he knows where she works. The quiet passion Lee lends to Carey’s reply, that he does not care what she does to make money, expresses Carey’s guilt but also his great sadness that his sister might feel shame about her job.

Chon and his actors pack so much into this simple scene, including suggestions of sexism and cultural expectations, that it emerges as a marvel of economy.

“Ms. Purple” is the kind of low-budget film, with inexpensive-looking slo-mo effects and an overwhelming score (the filmmakers anticipate any and all requests that the violins be cued) one usually sees only in local film festivals. Yet it played Sundance and is getting a theatrical release. This speaks to the quality of its performances, and to its truthful depiction of a bond that is universal yet so rarely explored on film.

M“Ms. Purple”:Drama. Starring Tiffany Chu, Teddy Lee and James Kang. Directed by Justin Chon. (Not rated. 87 minutes.)