Although Ah-Si never had to even lift his finger to get anything in his life, there was another reason why he was so easily beaten by Xiu. His heart didn't want to resist her. Something in his heart didn't allow him to resist with full force. As for why he cried... He was a sensitive person and Xiu's words weren't exactly nice.
The way she said things made his heart hurt badly to the point that physical pain had no effect on him. And the worst was done by Xiu when she dropped the bomb by telling him that Nora could never be a mother again. As if something in him died at that moment. Also, those words were enough to make him hate himself.
Xiu really didn't know what impact her words were capable of bringing.
Xiu could see his reaction but she didn't feel bad for what she did or said. No way! She wasn't gonna regret it. Not this time!