Seeing someone like Dedue actually have this kind of reaction is novel experience for him. He'd gained some measure of friendship and acceptance from the people that he went to school with, but this man is a stranger. Forgive him the surprise in his expression that he can't quite mask.

He holds himself back from falling into the more deferential posture, just letting his hands curl into fists at his sides in his tension. "I'm sure that as others get used to seeing me, it won't be terrible. I'm not expecting torches and pitchforks." He wants to think the best of people. To make friends where he can. They just have to get over the hurdle of first impressions.