Robin "Hope" backer
Can he sense light and/or darkness in this character?: Sure!
If yes to the above, what type of darkness?: Most negativity stems from being pointedly self-critical where he finds himself lacking. He tends to believe that as long as he works hard enough, he can achieve what he needs to and not let others down. When he doesn't do what he believes he should've or falls short, he's very hard on himself. Also might get some blips if anybody's competing with him and uses underhanded tactics because he frowns upon this nonsense. Hurt his comrades and he'll get pretty ticked - heck, hurt or sacrifice others in general and Robin won't be keen on you.

Also he was, you know, slated to be the vessel for the Fell Dragon. Kinda almost got bodyjacked, so that's probably there too.
Would he be allowed to make Unversed out of their darkness?: Of course.
Aggressive behavior (physical fighting, not sparring!) with this character: Could be interesting! Lemme know if you want to do something with it.
Injuring this character (include limits and severity please!): Don't kill him? That's about it.