Koi fairy wrasse, C. adornatus, would be my prime suspect, they are a pretty aggressive fairy toward other fairy and flashers, followed by the midas blenny. Most midas blennies are fine, but there are exceptions.
+1 on the Midas blenny. The one I tried was a major bully. My wrasses were terrified of him, as they should have been. He would land some brutal bites. He is no longer with me.
Maybe, maybe not. That's the thing with spinal injuries - sometimes they heal fine, other times they don't.
I lost my C. lineatus from a spinal injury. Not sure how he got it (I never witnessed bullying) but he passed that night. Here he was the day I noticed it. It was a sad day.