All comedy aside. This is a very thoughtful chapter! And an amazing one! They started opening up to each other in the sexual level, and of course as humans are, they have incompatibilities here and there, we can see it in how Mari-san not feeling comfortable doing it. And of course, when that happens, anxiety kicks in, all thoughts going everywhere, assuming this and that, venting to someone else. its very human for that to happen.
But, here's the thing. They all are assumption. If one wants the answer, then one needs to confront the partner, talks about it. Is it a hard conversation? Yes it is. And Arisa here, with all her positivity and wholesomeness just does it. IN THE PUBLIC! Just how a giga chad she is! And after that she gets rewarded with the "answer". And thus they can move forward with something they both are comfortable.
This chapter is a masterpiece in my book.