Kyoko's reaction manages to successfully pull out a very small laugh from Shinji, one that would probably last a bit longer if it weren't for Kai's comment. Instead, he ends up nearly choking on one of those laughs. Well done, well done.

"N-no... no, I'm sure it's just because that's how you two are."

Cute people doing cute things. A much more reasonable conclusion to come to, rather than trying to suddenly and incorrectly claim that he's the cutest one here.