Astarion isn't empathetic in any way that's useful or compassionate, really, but he knows pain. He knows exactly how it feels to be on the receiving end of this treatment - though the matter of informed consent makes it a bit hazy - and pulling those sounds from his lovely throat is a rush that he so rarely gets to experience. The guilt and the shame he feels in doing these things is still here, but it's a background hum, not a howl across his thoughts.

"Something a little different, then."

The next two blows, back and forth, stripe harsh lines across his ass - through his clothes, yes, but with a little more strength in his arm to make up for it. The third connects them, making two points of overlap which are going to really bruise.