There they meet, for the first time, their half-sister, 14-year-old Suzu (Hirose, whose unguarded, wide-eyed performance is one of the film's chief pleasures) and Sachi impulsively invites her to come and live with them.
Needless to say, the move is not without emotional repercussions, though not the kind an aunt warns of when she calls Suzu "the daughter of the woman who destroyed your family". Kore-eda, who wrote the gentle and contemplative screenplay, doesn't have soap-opera tantrums in store.
The film is slow to give up its meanings, which have to do with how love and good will can make it possible to come to terms with the regrets and hurts that we have locked away.
All this is contained in a package of Kore-eda's meticulous film-making, which uses the geometric interiors of the traditional house as the basis of sublime compositions in which characters are positioned as if in a painting, or through which they move in a refined but apparently effortless choreography.
It falls short of the masterly Still Walking and it's less formulaic than the director's most recent film, the swapped-at-birth story Like Father, Like Son, but it's still an accessible piece of work by one of the medium's great masters.
Review: Our Little Sister
Cast: Haruka Ayase, Masami Nagasawa, Kaho, Suzu Hirose
Director: Hirokazu Kore-eda
Running time: 120 mins
Rating: PG In Japanese with English subtitles
Verdict: Meticulous and ravishingly composed