Part of the cool look of FX’s hot new series “Legion” — debuting Wednesday, Feb. 8 — is the dewy, determined new face of Rachel Keller. Well, not so new to “Fargo” fans, who’ll remember her attention-getting performance as Simone Gerhart in installment two of the series.

Now she’s back in her biggest role yet, starring opposite Dan Stevens (yes, “Downton Abbey” fans, we’re talking Matthew Crawley) in this eagerly anticipated sci-fi suspenser from “Fargo” showrunner Noah Hawley. Based on the Marvel comics, the story follows David Haller (Stevens), a troubled soul diagnosed as schizophrenic — but is he? Or does the government just want him to think that he is? Enter Syd (Keller), a fellow psychiatric-hospital patient he falls for, who believes he may be more heroic (and powerful) than he realizes.

Keller, 25, graduated from Carnegie Mellon University. She lives in Los Angeles with her grandmother.

With all the twists and turns of this show, it had me feeling paranoid.

Joe! Just think what it’s like acting in it. [She laughs.] Here’s this guy who’s not sure what’s real and what’s not real. So how do we create an experience for the viewer that parallels that? We’re building something completely new. And if it’s a little disorienting, that’s kind of appropriate.

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There are people in this show who have certain powers. If you could have a superpower, what would it be?

I must’ve been a bird in some previous lifetime. I feel like I’m called to flying — the convenience and the beauty of it. That feeling of soaring would be empowering.

Dan Stevens is pretty fascinating in this — I don’t see a flicker of “Downton” in him.

He’s exceptional. He threw himself at this work, and it’s challenging. His role takes a level of sensitivity, openness and talent, and that’s what Dan has. That’s why his character is completely magnetic. When [series creator] Noah [Hawley] told me, “I think it’s gonna be Dan,” I said, “Ohhhh, I like that. I was a total fan of ‘Downton.’ ”

What was your first meeting like?

Dan and I had an afternoon in Santa Monica and it went on and on and on — we lost track of the time. You have to appreciate when you just connect with someone like that. It was like we were already friends, in a way. It’s not hard to be his friend. He’s not pretentious. But there was something special that happened when we met. We still talk about it — during difficult moments on set . . . we both realize we can rely on each other, as if we’ve known each other a while.

That’s great. OK — change of subject — how’s your grandmother?

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Well . . . [She yells to someone nearby.] Grandma?! How you doing?! [She chuckles.] I’m home right now. She’s going sailing, so she’s busy. She’s become one of my best friends. It’s been a totally surprising opportunity for both of us, now that I’ve lived with her for three years. It extended longer than we thought it would. And she’s great. Here’s a woman so full of love and incredibly nonjudgmental. I learn so much from her.

Why did you want to live with her? I mean, I’m sure she’s swell but . . . it’s an unusual choice for someone right out of college.

It was the best decision. I graduated and decided to come straight here. I couldn’t afford New York or L.A. on my own. You come out of school and you have a lot of passion and hope and drive, and yet you’re not sure how potential employers will respond to you. Moving in with her was interesting — it was a way of providing a place for myself that felt safe, and maybe a bit away from L.A. There’s a sheen over the industry, that I’m sort of resistant to.

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Living with grandma must feel more . . . real.

It allows me to be in L.A. but not in L.A., if you know what I mean. [Shouting to her grandmother.] “Bye, grandma . . . have fun!” She sails because she loves to sail. She talks about sailing the way I talk about acting. So, yeah, it’s a refreshing perspective, being here, especially when the business becomes too noisy and shiny.

You grew up in St. Paul?

I was actually born in L.A. My sisters and I were playing in a parking lot and my dad was like, “Nah, nah, nah. Let’s go give ’em some grass.” And Minnesota is beautiful — gorgeous summers, blustery falls . . .

And tough winters.

Yeah. My parents were really loving, open people to be around. I don’t remember them ever telling me this profession is difficult. There was never, “Uhhh, what else are you interested in?” They were just “Great. Done. Go for it.”