Sure, you had me at “Yakuza Princess.” But was there ever a more ponderous gangland saga set in the Japanese mafia than this?

It has a novel setting – the Liberdade neighborhood of Sao Paolo, Brazil, home to the largest ethnic Japanese enclave outside of Japan itself. And any yakuza story is going to pack gangland slaughter, gunplay and samurai swords wielded by over-tattooed, bellowing thugs.

But that’s about it. The Japanese-American singer Mazumi makes a sturdy if not particularly compelling lead. Jonathan Rhys Meyers was cast to give it a “name” in a role not really all that important to the plot.

And that plot! Whatever made the graphic novel this was based on worth a look steadily fades from view as our heroine, transplanted to Sao Paolo and raised there, visits first this person, then that one, and on and on, each of them sadly shaking her or his head because “I am not the one who can give you answers” but “This OTHER person you must find,” perhaps they can.

Akemi was the lone survivor of the slaughter of her grandfather’s entire clan back in Osaka. She was too little to remember what happened, whisked away to Liberdade where a collection of teachers and relatives raised her to work in a gift shop and train with a sensei in his dojo.

“Let DISCIPLINE shape your spirit and mind,” her teacher (Toshiji Takeshima) intones. “Let NOTHING come between you and your sword.”

On the day she turns 21, this American or Englishman (Meyers) , the doctors can’t decide which, wakes up in a Sao Paolo, his face and body covered in bandages hiding the stitched-up slashmarks, his memory gone.

The only thing that might trigger its return is the sword the cops say he was traveling with. Nope. Doesn’t tell him a thing. But he affects an escape and, not speaking a word of Portuguese, grabs that sword and stalks about Liberdade, a cut-up foreigner in a hoodie, toting a Katana sword on his back. Looking for…answers? Inconspicuous.

Back in Japan, Akemi’s secret has gotten out, and a grizzled yakuza (Tsuyoshi Ihara of “Letters from Iwo Jima” and “Thirteen Assassins”) hops on a plane to track her down.

The film’s first big action sequence has the yakuza, the American and a gang of local goons with a beef against Akemi all colliding, bloodily and terminally, in her apartment.

The fights are shot with more style and fury than anything else — lens flare (Digitally added?) and blood on the lens at every turn. The players are reasonable convincing in these brawls, even if we’re confused by the action and conflicting loyalties of most involved.

There are displays of torture, murder and finger-lopping yakuza loyalty tests, and the things these swords can slice off are sliced off, and often.

But our heroine takes forever to figure out what should be obvious early on, that grandpa wasn’t a “harmless old man,” even after the American asserts that “There ARE no harmless old men.” And even the twists that give Meyers’ character a reason to be here don’t pass that “Raiders of the Lost Ark” conundrum test. The story would essentially be the same without him here — the odd rescue and extra hand in a fight notwithstanding.

Mazumi’s handling of the fight choreography aside, it’s hard to see this as any great advert for her talents and future in film. She’s pretty, athletic but dull.

Not that “Yakuza Princess” fails on her account. It’s no great credit to anybody here, chiefly director and co-adaptor Vicente Amorin (Viggo Mortensen’s “Good” was his career peak), who has no feel for the material, no deep appreciation of the genre.

Rating: R for strong bloody violence, some language and graphic nudity

Cast: Masumi, Tsuyoshi Ihara, Eijiro Ozaki and Jonathan Rhys Meyers

Credits: Directed by Vicente Amorin, scripted by Vicente Amorin, Kimi Lee, Tubaldini Shelling and Fernando Tose, based on a graphic novel by Danilo Beyruth. A Magnet release.

Running time: 1:51