Japan’s voluminous comic book output yields the source for its latest animated film import, “Tekkon kinkreet.” This handsomely drawn and computer graphic-enhanced urban saga about two besieged brothers is a liberal adaptation of “Black and White,” a 1993 Japanese serial by manga (as Japanese comics are commonly known) auteur Taiyo Matsuomoto that spanned 33 installments for a total of 600-plus pages. Director Michael Arias’s woozy attempt to marshal the material betrays much crumpling, fraying, and loose ends, but it packs a few proportionately weighty payoffs.

Black and White are the actual names of the movie’s mercurial siblings, scamps hunkered down in the old district of a sprawling city. Black, a tormented teenager with apparent super powers, looks after the fanciful White, a toddler-like 11-year-old who still needs help putting on his shirt. The streets are their playground, not to mention a battleground with the mightier forces that loom over the low roofs of their beloved, grungy neighborhood, Treasure Town.

Gentrification is one way of describing the threat facing Black and White, but in “Tekkon kinkreet” that means yakuza shakedowns, twin cyborg assassins, and a febrile apocalyptic struggle. Clinging to the ideals of White’s innocence and the untouched old town, Black first fends off a strangely avuncular yakuza chief, Suzuki, and his lieutenant, Kimura. But the ultimate threat comes from Snake, an evil mastermind intent on paving the way to urban development.

The idea that two pesky kids provide Snake’s last major obstacle underlines how the battles raging within the young characters of “Tekkon kinkreet” are as important as those being waged on the ground. The movie’s torturous separation of Black and White during the course of their struggles festers into a raw, even disturbing expression of childhood’s end, scarier than the threats posed from the outside. The drawing style renders their faces as big ovals with tiny features, evoking balloons bursting from the strain. “All you need is love,” says the old-time gangster, Suzuki, in what becomes a refrain both macabre and melancholy.

“Tekkon kinkreet” is too compressed and rudderless to coax anything more than visceral emotion out of the brothers’ relationship, and the movie seems to drift in a fog with occasional blinding flashes. But one such extraordinary climax, which could have been even more powerful with a more skillful run-up, is Black’s fugue-like emergence from some inner hell. The painterly sequence of the film (think Francis Bacon) partly involves his taking the form of a minotaur and jolts the movie with the accrued impact of something originally developed over 33 installments.

Despite the harrowing showdowns, psychological or superheroic, that come front and center, one lovely achievement of “Tekkon kinkreet” lies in the background. The urban milieu, a mash-up postcard of traditional neighborhoods in Tokyo and elsewhere, is lovingly detailed and daintily colored, but much of this is easy to miss as the film careens about. Mr. Arias is an American expatriate, which fits the connoisseur’s care given to his adopted environs, and he’s voiced his ambition for the film to be “a hand-painted version of ‘City of God.'”

Mr. Arias appears to hold the distinction of being the first American to helm a “japanime” film, but his professional background seems more significant than nationality credentials. The filmmaker made his mark in animation software for honing CGI, after work on special effects and title sequences. But his inexperience with telling a feature-length story peeks through the cracks as the elegance of his film’s renderings and individual sequences are paired with a far less confident feel for large-scale storytelling.

In April, “Tekkon kinkreet,” a production of the well-regarded Japanese animation outfit Studio 4ºC (“Mind Game”), was honored with a North American premiere at the Museum of Modern Art. Parts of the movie are indeed like little works of art; if only the storytelling was realized with the same élan.