WARNING: The following article contains spoilers for Mortal Engines, in theaters now.

The post-apocalyptic adventure Mortal Engines has a sprawling cast, with Hera Hilmar's Hester Shaw and Robert Sheehan's Tom Natsworthy uniting with the Anti-Traction League in an effort to stop the roaming predator cities, such as London. Of course, the one-time capital of England has large population of its own, whom the usurper Thaddeus Valentine (Hugo Weaving) leads into war.

While many of those faces get plenty of screen time, the film's best character, Anna Fang, doesn't receive her due.

Played by South Korean singer/songwriter, Jihae, she oozes cool in so many ways. Anna makes her entrance with a shotgun, saving Hester and Tom from cannibals and slavers -- and in the heat of battle, we see her rocking swords and knives, literally hidden up her sleeves. She's basically a one-woman army, with director Christian Rivers painting her in a subtle light. He doesn't force her into the badass pilot role, as she's someone who isn't too loquacious; she prefers to speak with actions rather than words. With her sunglasses, punk hairstyle and kung-fu expertise, Anna is a blend of G.I. Joe's Snake Eyes and the Marvel Cinematic Universe's Black Widow.

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Her appeal doesn't come down to her style factor alone, however. She has substance, as we learn when she details why she's leading her squadron in the Anti-Traction League against the predator cities. In a crucial and rare moment of vulnerability, Anna tells Hester she was enslaved by the moving city called Arkangel, which is why she devotes herself to liberating others. She befriended Hester's mother, Pandora, and kept searching for Hester after her death. She's a heroine who puts others before herself, and isn't on missions of revenge like Hester and Tom. Anna was free from the system, but came back to save others.

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Sadly, those moments are few and far between, as Mortal Engines focuses on Hester, Tom and Valentine. Even when it comes down to letting Anna cut loose in battle, the movie shifts to Hester and Tom, who were still learning from how to become soldiers. That's highlighted by Anna's lack of screen time in the finale, when her squadron attacks London. She's pushed aside for Tom to become chief strategist, and it feels as if she's the apprentice. It's condescending, and doesn't fit the narrative, because Tom and Hester are so inexperienced. In a cliched move, the audience is force-fed the teenage lovers as the stars of the rebellion.

Anna isn't a main protagonist, but she ought to be leading the League's big plan at the end. Rivers does give her a quick fight against Valentine in the climax, but it's glossed over quickly and leaves viewers feeling shortchanged.

She's introduced much earlier in Philip Reeve's novel, and is a key player who's properly fleshed out, as opposed to feeling like a throwaway character on the screen. In fact, her character in the film is so interesting that, after meeting Jihae, Reeve went back and wrote a prologue novel about Anna. It was published in July, and now he's contemplating doing a prequel comic devoted to the character. Hopefully it sees the light of day, because in her few scenes, Anna definitely steals the film.

Directed by Christian Rivers, Mortal Engines stars Hera Hilmar, Robert Sheehan, Hugo Weaving, Jihae, Andy Serkis, Ronan Raftery, Leila George, Patrick Malahide, and Stephen Lang. The film is in theaters now.