[KyleGoetz]

I've never read Naruto or watched more than one episode, so I don't know. I've never heard of 忍 as a counter for ninja or anything, but I'm not the final arbiter of that issue. However, my dictionary does not have that as a counter for ninja, and I can't imagine there being a counter for such a narrow class of terms. It's probably an abbreviation for ninja in Naruto, but since I've never seen it, I can't say for sure. I defer to someone else on this issue.