Maha Harada spent two decades building scenes on the page before she ever stood behind a camera.

Now 64, the best-selling Japanese author is making her feature directorial debut with “In My Father’s Room,” a film adapted from her own short story “An Unnecessary Man,” and it arrives in competition at the San Sebastian Film Festival before moving on to the Busan International Film Festival.

Ahead of both stops, Bitters End has already sold the film to France, Korea, Taiwan and Hong Kong, with more territories under discussion.

The transition from novels to film feels less like a leap than a continuation, Harada says. Her years working as a museum curator shaped how she writes long before she considered directing. “When I write fiction, I tend to depict scenes and the characters’ inner lives as if looking through a camera,” she says, adding that adapting “An Unnecessary Man” felt natural because the story is set in a town she once lived in and can still picture in exact detail. She describes the short story as an ordinary, universal story of a father and daughter, deliberately free of mysteries, schemes or sensual drama.

That story follows Satomi, an art museum worker who learns almost nothing about her father, Yuichi, until after he has died alone. Harada says the character grew directly out of her own family. Her father sold art books, loved film and gambling, and “never stopped causing trouble,” she says, but he also introduced her to Picasso at age 10 and took her to see “Gone with the Wind” and “The Castle of Sand” at 12. It was only once he was gone, she says, that she understood how much he had taught her.

Central to the film is the idea that Yuichi’s value cannot be measured by his usefulness to society, a theme Harada says she wanted to explore directly. “Whether or not you’re happy is something you decide for yourself,” she says, arguing that a life spent pursuing things whose worth is apparent only to oneself can still be a happy one, however little it resembles society’s idea of success. She adds that Yuichi’s willingness to die alone, having chased only what mattered to him, could be seen as extreme, but says no one can call his life anything other than happy.

Visually, Harada built the film around two anchors: the Japanese tea ceremony, or chanoyu, and a painting by Mark Rothko. She wanted to bring the ceremony’s quiet, everyday symbolism to the screen, and to pair it with Rothko’s work as a Western counterpart to that same sense of beauty. She notes that Japanese museums collectively hold 10 works by Rothko, acquired by curators who recognized the artist’s spiritual quality decades before his prices climbed, a fact that still makes her proud.

Moving from prose to a film set meant giving up some control, Harada says. Before filming began, she recalls, her assistant director read the script and asked her, “Isn’t there too much stage direction?” The comment made her realize that a novel is, in her words, almost entirely stage direction, with the writer controlling every detail the reader sees. On a film set, other collaborators have to be given room to interpret. She trimmed the script accordingly, and after being told there was “still too much explanation,” cut it further on set, ultimately paring the dialogue down to very little.

Working with Yu Aoi, who plays Satomi, and Issey Ogata, who plays her father, Yuichi, reinforced that shift. She singles out a scene where Satomi comes home after being laid off and simply leaves the tap running, calling it a moment where Aoi conveyed despair through almost nothing at all, and says she sometimes forgot to call “cut” while watching her work. Ogata, she says, gave Yuichi a lived-in warmth, playing a father with no money or status who never lets go of the things he cares about most. She calls his performance of the tea ceremony one of the film’s biggest highlights.

Cinematographer Yoshio Kitagawa, whose earlier credits include “Evil Does Not Exist,” shaped the film’s look alongside Harada during visits to tea ceremonies and museum viewings of Rothko’s work. She points to Yasujiro Ozu and Victor Erice’s “The Spirit of the Beehive” as touchstones for the film’s tone, and to Kei Kumai’s “Death of a Tea Master” as a specific visual reference for the ceremony scenes.

Harada says reaching audiences outside Japan has been the hardest part of her writing career, even as her novels have found readers in South Korea, China and Taiwan. Entering the film world at 64 was partly about proving that age should not limit what someone takes on, she says, crediting the cast and crew who stayed with the project throughout.

Having adapted and directed her own writing once, Harada says she is open to doing so again, though the idea of writing something built specifically for the screen, rather than adapting an existing novel, had not seriously occurred to her before now. She calls the process of directing “In My Father’s Room” a dreamlike experience unlike anything else in her career. “If this is a dream, I hope I never wake up,” she says. Asked what comes next, she says she plans to keep writing novels alongside directing more films, rather than choosing one path over the other, adding that doing both will make things twice as hard, and, she believes, twice as wonderful.