Pedazos translates to "pieces" or "fragments". While seemingly simple, its use here is quite evocative and goes beyond a literal meaning.
In the song, Zahara sings, "De pequeños pedazos del otro" (Of small pieces of each other). This metaphor beautifully conveys the idea that the two individuals were deeply intertwined, almost as if they were made up of parts of one another, highlighting the intensity and eventual fragmentation of their relationship.
"Guerra Y Paz" opens with a couple built from the same material: "Tú y yo estábamos hechos" ("You and I were made"), and the rest of the song is Zahara trying to remember what they were made of. She can't recall the color of a shared smell, whether it felt like acid or metal, whether it was war or peace between them, which is where the title comes from. The chorus keeps landing on "No consigo recordar" ("I can't remember"), less like sadness than a kind of panic: forgetting the good parts of someone feels like losing them twice.
Santi Balmes answers from the other side of the same breakup, and he gets the song's sharpest line: "Unos pulmones que ya no respiran por ti" ("Lungs that no longer breathe for you"). It's blunt where the rest of the song stays foggy, and it explains why she keeps asking "¿Cuándo volverás a ser quién conocí?" ("When will you be who I met again?") - she isn't waiting for him to come back. She's waiting for a version of him that already left.