Harley's kick connects and Kain is brought down, only managing to get back up into a bent over position as the throbbing pain hits him. He keeps grip on his weapon, but just barely. The mental assault is making this a whole lot worse, weakening his resolve. All he can do at the moment is take a defensive position, trying to gather enough strength to deal with them.

"And if I refuse? Some people must have managed to fight off their power. What makes me different, surely... is how much stronger I am."

Except he doesn't feel too strong right now, not when he's thinking about how much easier it would be to let go and allow the darkness free reign.