It takes some time while Yamazaki spots out the white-haired kid who just made his evening turn to a kind of nightmare not too long before and first he thinks of running away or hide somewhere, but this would be childish, even from him. So he waves to Sai and smiles at him (hoping that this makes him bored enough to leave him alone.)
Screams. In joy, of course.
"Oh...hi, Master. Are you lost?"