Focus on pain that isn't visible. "You see the smile, but you don't see the stitches underneath / I'm walking through the fire with ice between my teeth."
Since the beat is titled "Wounds," the lyrics should focus on healing, scars (both physical and emotional), and the passage of time.
If you're still tweaking the instrumental, focus on these "sad" production tropes:
Layer in sounds of rain, distant thunder, or paper tearing to add texture to the "Wounds" concept.
To help you develop content around the theme for a sad piano rap beat or deep hip hop instrumental, here are a few creative directions for lyrics, visual concepts, and promotion. 1. Song Lyrics & Themes