Aha, awesome! I will....probably end up backtagging that even though I owe you fifty million tags already. orz
He does have an aversion to using his magic openly, yup! And no, he didn't give it up to Yuuko, though he did give her the tattoo on his back that restrained his magic.
In the manga, he was shown to have used his magic when the lives of people he actually cared about were in danger, though if it was just him at risk, he wouldn't bother using it. Even then, it'd only be at risk of death and for someone who wasn't capable of protecting his/herself. So I assume the same would hold true here in the dome. Using magic would leave traces of it behind, and increase the chance of his Ashura finding him and that would be baaaaaad.
But one day, I'll force him to use it. Once he makes friends. *cough*
ANYWAY. Sorry for the tl;dr.
What is it about a character that makes you want to app them? Weirdly worded, but I guess why do you app the characters you do?