Was this a good thing? Shura doesn't quite know. If Yukio was training to obtain aria and knight meisters, than was he still considering defecting? Or was this all part of his manic quest for strength?

"Ain't you ambitious!" She's still in a bit of a shock, but she won't let Yukio leave her behind. She won't rush to catch up with him, but slightly lengthens her stride to make up some of the distance. But really, teach Yukio? If Shiro could see them now, he'd probably be laughing. "If you're really that set on learnin', I guess I could show ya a few things."

For all that she wanted him to take a break and had absolutely no interest in teaching, Shura knows when to take advantage of an opportunity when it showed itself. And even if he wasn't just calling her bluff to mess with her, he didn't have much room to back down from his bluff if he wasn't serious.