It's easy for Kuroo to ask for a verbal answer- Tsukishima doesn't have that commodity. And if Kuroo's voice is shaking, then Tsukishima's is in tatters, which is why he resorted to not answering- Kuroo will tease him later about it. Still, he answers a stuttering "...yess..." because the spot on his neck is being abused by warm lips and he can feel himself wanting more than just simple kisses.