Once the pair got into the groove of things it really wasn't hard to get across the dance floor only a matter of time. The notes were remarkably lenient towards Blue's completely out of time shuffling and whatever the heck it was Kat was doing. It could really only be called dancing in the vaguest of senses but it was movement in time with music and Kat was making her way to the door.
When they made it to the other side of the room the barrier was still up, Kat was tempted to break through but a "Just wait out this song," from Blue when she spotted Kat's actions was enough to still Kat's thirst for violence, especially considering it wasn't really all that high. Punching things just happened to be a good answer to problems since she'd become a demon.