The haunting “Lullaby for a Soldier” performed by actress Maggie Siff for the TV show Sons of Anarchy was used to memorable effect on the trailer for Twentieth Century Fox’s Alita: Battle Angel, a Dec. 21 theatrical release directed by Robert Rodriguez.

“I didn’t know what to expect when Maggie came over to the studio,” Bob Thiele, music supervisor and composer for Sons of Anarchy, told Rolling Stone. “She said rather humbly that she ‘could sing.’ As you can hear for yourself, Maggie has a beautiful, captivating voice. For the actual track, I felt that any instrumental accompaniment should be minimal. Even a small acoustic guitar seemed to distract from emotional tone of her performance. I wanted nothing to interfere with the power of her vocal.”

The song was written by Dillon O’Brian for the motorcycle gang drama and is included on the 2013 soundtrack release Songs of Anarchy, Volume 3.

The trailer for Alita has received more than 7 million views since Fox posted it to YouTube in December, with a great many of the comments swooning over the song. Tom Holkenborg is composing Alita’s original score under his DJ handle Junkie XL.

Battle Angel is an epic futuristic adventure in the story of a girl, Alita (Rosa Salazar), who awakens with no memory of who she is in a world she does not recognize. Taken in by Ido (Christoph Waltz), a compassionate doctor who realizes that somewhere in this abandoned cyborg shell is the heart and soul of a young woman with an extraordinary past. As Alita learns to navigate her new life and the treacherous streets of Iron City, she realizes she has unique fighting abilities that may be the key to saving her friends, her family and the world she’s grown to love in a fight against hostile forces.