"Then why do you care so much about ensuring I suffer?" If he didn't care how Kuai felt, then why bother tormenting him?

He was still on the defensive, though he'd lowered his guard somewhat. This was likely another trick by his brother to get Kuai to leave an opening where he could dash in and eviscerate him. He was doing a fairly good job of that with words alone.

"I was never going to live up to your impossible standards. I've known that since I was a child."