Brief consideration, not even turning to fully face her as she appeared, Kylo Ren shrugged. "Lets spar," he said in his usual even, cool tone. "I'd like to see how we compare; then we can better train against our weaknesses."
Unlike Katherine, he didn't wear any sort of protective clothing or armor. If he took a hit then it was his own folly and should suffer the consequence of it. While her blade might leave a mark, even crack the flesh if she struck hard enough, he had bigger things to worry about against a lightsaber--losing entire body parts, for instance. He wouldn't be hit, however.
Kylo Ren took one step away, blade still down at a slight angle. He gave Katherine several seconds to prepare before he made first strike, bringing up the heavy longsword to take it by two hands and sweep forcefully down in her direction.