One hour into “Alita: Battle Angel,” the Robert Rodriguez/James Cameron adaptation of a popular Japanese graphic novel series, the combat gets funny, the dialogue snappier and the trash talk flippant and smarter.

We just have time to wonder “Where has this wit, this tone, been until now?” when it’s gone again. And the visually striking, manga-inspired movie mash-up settles back in for another tedious hour.

The “Sin City” director and “Avatar” and “Terminator” co-writer and producer always give us dazzling visuals, and the eye candy here is first-rate, an integration of human actors and their motion-capture animation avatars that is a step beyond “Avatar.”

But Cameron’s plodding storytelling and tin-eared dialogue — The catch-phrase here is “You underestimated me.” I can see the T-shirts now. — overwhelms Rodriguez’s lighter touch for a movie that plays and feels like an ungainly Frankenstein lacking the humanity that might give it life.

I can’t speak to the manga that inspired it, but Cameron, Rodriguez and third screenwriter Laeta Kalogridis give us settings, characters and story elements from “Blade Runner,” “Robocop” and “Rollerball,” all hanging from the framework of Cameron’s TV series, “Dark Angel.”

Whatever comfort these over-familiar tropes deliver, “surprise” and “invention” don’t figure here.

Five hundred years hence, “three hundred years After the Fall,” Earth is a crowded, crumbling but functional dystopia where The Singularity seems to have set in. Most people have varying levels of machinery grafted onto their persons.

We’ll get to the “sexless future” this sort of dystopia suggests and popularizes in movies of this genre later.

Dr. Dyson Ido (Christoph Waltz) keeps the assorted worker drones, street toughs and bounty hunters of this lawless “technarchy” going. And in his spare time, he rummages through the hi-tech garbage dropped from the last sky city floating above his home here on the ground, Iron City.

That’s where he finds the remnants of a teen girl cyborg whom he names Alita and re-assembles. Alita (Rosa Salazar of “Maze Runner” and Netflix’s “Bird Box”) “wakes up” with a lot of memory loss. But her new “father” lets her play outside after imparting just the occasional life lesson.

“People do terrible things to each other here.”

Such as scavenge parts off their fellow cyborgs or carve up flesh and blood humans whose organs, we figure, wind up re-used in Salem (pronounced “Zalem” here), the oligarchical promised land floating just over their heads.

Alita meets cute, souped-up unicycle driving hustler Hugo (Keean Johnson of TV’s “Nashville”). He takes a shine to the “hard body,” hangs out with her and teaches her about the popular, no-holds-barred motorized roller-blading sport of Motor Ball.

The masses LOVE Motor Ball. Champions there have the promise of making it up the drooping pipelines that take people and supplies up to Zalem.

Alita has a warrior past which shows up in martial arts form when assorted murderous scavengers and hunter-warriors menace her and her new “family.” Instincts are programmable, but mental flashbacks show her the soldier’s life she used to lead, battling on the moon or Mars.

Chiren (Jennifer Connelly) is another cyborg-fixing doctor who takes notice of who Alita is and what she was. Local “Factory” boss Vector (Mahershala Ali) keeps siccing his motorized man-mountain (an unrecognizable Jackie Earle Haley) on her, and Zapan the hunter-warrior (Ed Skrein) is always pulling out his “Damascus Blade” (guns are banned) and trying to take Alita’s head off.

They’re all staggering forward to the Big Game/Hunger Game/Rollerball finale where they’ll settle scores on the track.

The fights — and there are many — are even more technically impressive than the interface between human actors and animated ones. If it’s physics-defying combat (Alita leaps and changes trajectory, mid-leap, from time to time) you want, “Alita” is hard to top.

But they introduce us to a world that feels barely sketched-in — a polyglot of races, languages (as in “Blade Runner”), technology and government by “Factory.”

The Alita-Hugo romance has, technically and romantically, nowhere to go, and Johnson, acting opposite a leading lady wrapped in a motion-capture suit, fails to generate any hint that it can.

Alita is an impressive creation, with huge anime eyes, a perfectly-contoured face (a little scar on her nose, pores) and minimal emotional expressiveness. Whatever the limitations of the technology, at least a little of that falls on Salazar. It’s got to be daunting “acting” under these conditions. The body motion is a lot more natural looking.

Among other cyborgs motion-captured by real actors, Skrein, Michelle Rodriguez and Jeff Fahey are recognizable, though none are really wholly developed characters.

Of the supporting cast, only Connelly makes much of an impression — icy, heartless, posed in futuristic lingerie in one scene, “Alita’s” sole suggestion of sex.

So back to that “sexless future” thing. Manga got its start in Japan, first described by Western outsiders as “comic books for grown men.” The fantasy worlds woven with their pretty boy heroes and eternally school-girlish heroines have proven to be catnip to a worldwide audience, including North America.

Anime and video games have deepened the immersion into this obsessive cosplay-friendly fantasy world, but with consequences. The “sexless future” that the chaste, adolescent romance of “Alita” portrays seems to be a part of that appeal, pandering to those looking for an emotional remove that lumps the film in with online avatar “hook ups,”  guys with lifelong schoolgirl fantasies and sex-with-dolls-until-we-can-have-sex-with-robots dreams.

In Japan they have a name for the arrested development men (mostly) who go deep into this cosplay lifestyle — Hikikomori. A plunging birthrate there is at least partly blamed on this addiction and the infantilization that often accompanies it.

Cameron and his fellow screenwriters altered and Americanized this Japanese tale (that always had American settings), but not that permanent pubescent American Hikikomori appeal. Because nobody knows what fanboys want better than JC.

“I will not stand by…in the presence of EVIL.”

But they’ve made a movie where they can crow about the technology and the eye candy they deliver, conveniently skating past the chilly inhumanity of it all and ignoring its quasi-perverse asexuality. They may have a new franchise on their hands. It’s a pity they’ve manufactured one without a heart.

MPAA Rating: PG-13, violence, sci-fi action, profanity

Cast: Christoph Waltz, Jennifer Connelly, Keean Johnson, Mahershala Ali and motion captured versions of Rosa Salazar, Ed Skrein, Michelle Rodriguez and Jackie Earle Haley, Casper Van Dien

Credits: Directed by Robert Rodriguez, script by James Cameron, Laeta Kalogridis and Robert Rodriguez, based on the Yokito Kishiro graphic novel series “Gunnm. A 20th Century Fox release.

Running time: 2:02