“Knights of the Zodiac” is an adequately-budgeted action fantasy about young warriors recruited to protect or attack the reincarnation of the Greek goddess Athena, warriors identified by their connection to an inner power/”Force” called Cosmos.

No, it has nothing to do with the science TV series based on the book by Carl Sagan. Yes, it has a lot of similarities to every other YA sci-fi/fantasy thingamabob that’s ever come down the pike.

Based on a manga/Japanese comic book series, it isn’t cast and played as “young” as say “Percy Jackson and the Olympians.” But it’s still pretty childish in its setting, derivative plotting, actions beats, heroines and heroes.

Japanese American singer-actor Mackenyu — please don’t make fun of the name, or the fact that this chap figures he gets to go by one name when his level of fame suggests maybe that’s an overreach — stars as Seiya, whose older sister was snatched when he was a child.

He got a hint of her “Cosmos” power when he grabbed at her magic medallion necklace one time. As a haunted adult, he’s still looking for her, and of course cage-fighting in an underground octagon to make ends meet.

Just as he’s getting his butt whipped by the brute Cassios (Nick Stahl), he summons up that dormant power. That alerts rich-guy recruiter Alman Kido (Sean Bean) to his existence and whereabouts, and summons the minions of Alman Kido’s sinister ex-wife Vander Guraad (Famke Janssen).

In a flash, our hero has to choose a side, which of course means he’ll be taken in by the guy protecting the new goddess Athena, born Sienna (Madison Iseman), a spoiled “rich girl” to Seiya. He’ll have to train, learn to use his powers, ponder the mystery of his missing sister, resist the temptations of Vander Guraad and eventually “save” Athena when the chips are down.

Or not.

The fight scenes have cool slo-mo effects, and the best of them come from the pre-“Knights of the Zodiac” armor that Seiya acquires as he masters his powers. The octagon action has some decent wirework — spinning, floating kicks and what not.

The acting is never really bad, just indifferent. Even old pros Bean and Janssen can’t summon up much enthusiasm for this silliness. Mackenyu shows off a few martial arts moves early on. But once you’ve got magic powers and armor, the brawls turn “Transformers” dull and CGI.

The running “gag” is “You don’t know when to quit, do you?” And the rest of the dialogue is either too bland to bother quoting or standard issue “You should have DIED when you had the chance!”

The limited sci-fi “tech” we see is mainly this Opsrey-styled jet-powered transport.

Fans of the comics will certainly get more out of it than newbies like me. All we see is all the other middling YA sagas it resembles, borrows from and fails to match or improve upon.

Rating: PG-13, violence

Cast: Mackenyu, Famke Janssen, Madison Iseman, Nick Stahl, Diego Tinoco, Caitlin Hudson and Sean Bean

Credits: Directed by Tomasz Baginski, scripted by Josh Campbell, Matt Stueken and Kiel Murray based on the manga/comic series by Masami Kurumada. A Sony release.

Running time: 1:5