Set on the Pine Ridge Reservation, "War Pony" began as a project among friends and over seven years grew into a community effort, said directors Gina Gammell and Riley Keough, who presented their directorial debut at the Cannes Film Festival.
Cast entirely with first-time actors and set in the sovereign lands of the Oglala Lakota in South Dakota, the movie follows the setbacks and triumphs of 12-year old Matho, played by LaDainian Crazy Thunder and Bill, 23, played by Jojo Bapteise Whiting.
"It started with us making a film with our friends," Keough told Reuters of a project with roots going back to 2015 when Keough met Bill Reddy and Franklin Sioux Bob, who were working as extras on the movie set of "American Honey".
She bonded with the pair and, along with Gammell, suggested they tell stories about their lives through a film.
"How to collaborate responsibly between communities ... sort of became our mission," said Keough, describing a process that included writing workshops, improvisation sessions and meeting hundreds of people to build a local cast.
"These are not subjects of a film, they are our very close, dear friends and family at this point."
Sioux Bob, meanwhile, hopes the movie can also be a catalyst for change.
"This story is a Native story told by actual Native voices. I hope this can be a project that breaks down doors," he said.
The film's showing in the "Un Certain Regard" category at Cannes carried extra resonance for Keough, with the forthcoming premiere of Baz Luhrmann's film about her grandfather, Elvis Presley, also at the festival, she said.
"I think that everything kind of happens for a reason," Keough said, adding that she thought Luhrmann did "an incredible job telling our story, our family story".