No matter how fervent their fans may be for a movie adaptation, novels called unfilmable get that tag for a reason. Confronted with a masterpiece’s thickets of character and tangles of prose, filmmakers too often either hack away or make something faithful but unwatchable.

Indie veteran Gakuryu Ishii took his own dark comic approach to Kobo Abe’s “unfilmable” 1973 novel, “The Box Man,” whose titular protagonist scuttles around Tokyo in a dirty cardboard box and scribbles his pensees in a tattered journal. Imagine an intelligent, literate, half-mad hermit crab.

After his 1997 attempt to film “The Box Man” failed — key financing fell through — Ishii put the project aside for decades. He finally shot it with two of his original stars — Masatoshi Nagase and Tadanobu Asano — based on a script he co-wrote with Kiyotaka Inagaki that makes the novel’s philosophical musings and metaphorical conundrums more audience-friendly while not dumbing them down.