Cruzada literally translates to "crusade," a strong and historically significant word. It's not a common term you'd find in everyday Spanish songs, making it quite unique and memorable.
In the context of the song, the artist sings about "Empezando esta cruzada" (Starting this crusade). Here, it's used metaphorically to describe a difficult and determined journey or struggle, likely referring to the emotional battle of moving on from a relationship. This powerful imagery makes the word particularly enticing.
Nil Moliner's "El Aire Que Me Mata" is a powerful song about breaking free from a toxic relationship. It's all about finding the strength to walk away when someone else's negativity is literally suffocating you. The singer is done waiting around, saying "No voy a esperar sentado tus palabras a pedazos" [I'm not going to wait sitting for your words in pieces]. He's ready to move on and rediscover himself, even if it means walking a path alone.
He feels like the very air around him is killing him because it's extinguishing the light in the other person's eyes: "Es el aire quien me mata porque acaba con la luz de tu mirada" [It's the air that kills me because it ends the light of your gaze]. It's a really vivid image of how draining this relationship has become. He's tired of wishing for things to change, "Cansado de pedir siempre un deseo" [Tired of always making a wish], and is determined to leave this "infierno" [hell] behind to find his own way.