"What if Warrior Cats was a Southern American detective drama? This is a Warriors version of opening to the HBO series True Detective. Maybe that combo doesn't make much sense, but I loved this opening so much I needed an excuse to reproduce it." Video Link. Original True Detective open is here.
And that lovely song is the Handsome Family's "Far From Any Road," from the 2003 album Singing Bones.
(Thanks to all who suggested!)