I kind of got this idea after watching B.A.P's Japanese Warrior MV making.  Yongguk appeared to have a scar underneath his right collarbone.  I Googled it, wondering if he'd been hurt recently or undergone surgery for something, but I found nothing.  I was just perplexed by it, and because I couldn't find out anything about it, I just kept thinking about it, and then this fic came to mind.

Here are some (not so good) images of Yongguk from the MV making.  The scar is a light red/pinkish line starting from around the middle of his chest, right below his collar, and moves down and towards the right.  The full extent is not shown.  I do NOT own these images.

Here is the best image of it:

Even a GIF:

Does anyone know what this scar is (if it even is a scar) or where it came from?