"So it will be faster if you do. Your quirk is powerful. Maybe you can figure out how to make it painless."

Kaworu's expression and tone aren't angry or pleading. It's decidedly a restrained persona that he's adopted. Because he needs to, he can feel the corruption swirling inside of him and it rises in this place and when he thinks about the Old Man and how he's been unfairly taken from Kaworu. So instead, he just focuses on the mission at hand.