That sounds... cute. Not just the idea of Rin dancing ballet (he does have a very clear picture of what ballet looks like, in his head; interesting), but the idea of a kid liking to teach, too. Sarge knows that feeling.

He finds himself smiling a little, back, and then collecting both glasses that the ghost delivers. One is clearly for Rin, so he leans down a little and offers it to it. "Sure, if Fio's okay with it. I know there's some kind of dance I know how to do. Maybe it'll be that."