Parca refers to the Grim Reaper or personified Death, often depicted as a cloaked figure. It's a more poetic and less common word for 'death' than muerte.
In the song, the lyric "Nadie de la parca se puede escapar" (No one can escape the grim reaper) delivers a powerful and somber message about the inevitability of fate, especially in the context of the violent life described in the lyrics. This word adds a dramatic and memorable touch, making it stand out.
"El Karma" tells a gritty, tragic story from beyond the grave. Mexican artist Ariel Camacho sings as a narrator who starts out in Agua Caliente, moves to Culiacán, and gets into the underworld—or el ambiente ("the scene")—to make money trafficking in Los Angeles. Trouble starts when rivals try an express kidnapping on his daughters. The narrator is fiercely protective and furious, noting that nobody gets to put a price on his family. He tracks down the kidnappers to settle the score, kicking down the door with his Browning pistol ready to go.
Things go south fast. The narrator walks straight into a trap—el cuatro en la mesa (literally "the four on the table," meaning an ambush). He fires his gun, but an R-15 rifle cuts him down. What makes the track hit so hard is the fatalistic twist at the end. Even though the narrator dies, he points out that karma always circles back: the person holding that R-15 is now dead too, because "nadie de la parca se puede escapar" ("nobody can escape the Grim Reaper").