[He plays it especially well considering that was a lot of heavy emotions for a creature not used to them. He'd protest using the word "shaken", but... perhaps at first he reacted more automatically to the familiarity of Ciel's tone, and only registered the change in his soul several seconds later.
A small, deferential nod. You are.]
And I always your faithful servant. [Always. Including mere seconds ago. A faithful servant only ever acts in his master's best interest. The unsteadiness is noticeable, and even if Sebastian backed off it only means he's no longer so horribly close; he can still reach out his hands, meaning to steady Ciel.]
Here. Please come. [Nevermind that Sebastian still looks a mess of drying blood. Come, let him carry you.]