You know what I want to see in this series? I want to see Yamada put Kase-san on the back foot, romantically speaking, like be the one to make her flustered or plant a surprise kiss on her or something.
Yamada with a little confidence in the relationship would be an awesome sight.
Well, she did this by accident, in some way.
When Yamada told Kase that she never had any relationship before and that there sure is "stuff that's supposed to be done" I'm pretty sure Kase misinterpreted that and though Yamada was talking about physical intimacy.
The story is, after all, mostly written from Yamada's perspective and she'a little naive, but I think Kase had some cheeky thoughts on several occasions already: When she tied her new shoes I think Yamada actually felt correct: Kase couldn't resist and wanted to take a peek... also the thing with the "indirect kiss" and the water bottle
Kase's not a perv and all her actions were cute & sweet so far, but if Yamada stays this dense to Kase's attraction towards her her girlfriend might blow up at some point and advance a little more... (though I doubt it would be a full push down or the like. Kase's way too nice & honest for that). She might even openly talk to Yamada at some point (as in "hey, just making sure, you really feel the same way... right?")