[he knows that response is neither positive nor negative, but Kaworu is such a mysterious person that Nageki quite sure this is something he'll have to press for at least a little if he wants to know what it is that's bothering his friend. pressing for anything isn't in Nageki's nature at all, but there are some things in which he knows he could stand to change. maybe that could be one of them.

if Kaworu makes it obvious it isn't something he wants to talk about, Nageki will stop. that seems simple enough to him, or at least Nageki hopes it is as he sits down on the piano seat next to him.]

It's as though something is bothering you. Your thoughtfulness doesn't look like the happy sort to me... but I could be wrong, I course.