Sigourney Weaver says working with James Cameron on the Avatar series is "like the perfect job for an actor": "He does everything possible to make sure you get to try everything you want to try"

Kiri is no ordinary Na'vi. Born from Dr. Grace Augustine's Avatar, Kiri has been adopted by Sam Worthington's Jake Sully and Zoe Saldaña's Neytiri and has grown up alongside their children, but it's clear there's something very special about this unconventional child.

Sigourney Weaver, who played Dr. Grace in Avatar and returned as Kiri in The Way of Water, is back once again as her teenaged character in Avatar: Fire and Ash, which explores Kiri's mysterious, mystical connection with Pandora's goddess Eywa in greater depth.

"Well, it's interesting because we're also not necessarily working in continuity," Weaver tells us when we meet in London to talk about the film. "So Kiri, who I think has these gifts, I guess you'd call them: an ability to communicate with other species and to somehow create miracles. And she's just – as far as she's concerned – a kid. A kid [who] doesn't know who her father is, etcetera. And in this [film], because all hell breaks loose, she has to step up, and she kind of has to go, 'All right, I'll never understand it, but I've just got to do what I have to do, and somehow I'm capable of doing [this].'

"And I think it's amazing to see that power take hold of her and change her, and kind of educate her," Weaver continues. "And you see that growing throughout the film. And so it's almost like, at this point as an actor, when I walk into the Volume where we do this work, I know the character, she's in me, but I have to kind of get out of her way, because I have no idea at this point. I do a lot of preparation ahead of time, but when I walk into the Volume, I sort of go, 'Okay, Kiri, take it away,' because she's so much a creature, an animal, as well as a human girl, that that part of her I just leave to [her]. I think your mind is saying, 'You're not this,' and my instrument is saying, 'Let's go!'"

Weaver of course is a frequent collaborator of director James Cameron's, beginning with 1986's Aliens. "I think he basically said, 'I hope you can do this,'" Weaver says with a laugh of working with Cameron on Fire and Ash. "Because we shot two and three together, and, of course, casting someone my age as someone 14, we joke about it, that I was this age emotionally, thank you very much! But I think he did see something in me that must have helped him create Kiri, and he just wanted me to get on with it.

"In fact, I don't really think he tells us where we're going. He wants to find out through us where the character is going, and that's why he's not in video village or anything," Weaver adds. "He is right there with us. And when we get to a scene, we are genuinely there to find out what the scene is about. And for Kiri, it's often, 'How does she make sense of what's happening now? How does she make sense of this world that doesn't make any sense to her?' And so, he kind of helps you get out of your way. He does everything possible to make sure you get to try everything you want to try. So, it's kind of like the perfect job for an actor. It's kind of a dream job."

You can see Kiri come into her own when Avatar: Fire and Ash arrives in theaters this December 19. In the meantime, check out our guide to the biggest movie release dates of this year and beyond, or catch up on the previous film with the lowdown on the Avatar: The Way of Water ending explained.