@fluffjunk13 She probably overheard what he defined their relationship as. It shouldn't be surprising to her, given all the issues she has trying to get him to open up to her.
I'm on Junta's side here - if i were him, i'd call that relationship anything but "friendship". Especially with his self-esteem and "partial invisibility" (ehm... not DooM one).
But they do have chemistry between each other. Especially from Nagisa's side.
Not going to pretend I'm some art critic, but it seems like whenever we see our MC 'progress' in this story/relationship we get a panel with our MC drawn in more detail, totally different than the aloof, mob character we normally see him as. Maybe we'll see him 'evolve' by the end of the story from a straight up mob character that gets chibi-fied(?) into more panels like this where it shows off some of his characteristics.
Cute Saki. Cute Shiraishi. Cute Kubo. I wanna hug all of them.
@friedtofu That's a good touch, and there are a lot of ways to interpret why he becomes like that when they progress. For a moment, he's not a mob, or becoming more than one, or a perspective change to show how she sees him even if he is one.