There's a bunch of interesting bits of info that can be gleaned from the art.
As some have already mentioned, Sabu is pushing hard the notion of Matsuri and Harumin being foils of each other from the way she keeps drawing them in mirrored panels, like on page 12, a subtle way to let us know that they're more alike than they think. Another bit that caught my attention was how Matsuri's intent taking Harumin to her room was to probe if Harumin was there of her own volition (and thus, finally showing she cares about her) or if she was doing it to keep the facade of a model student. Initially, Harumin implied it was something she did for obligation leading to the very disappointed Matsuri of page 2. I'm convinced that Matsuri would've tried to pull a Mei and essentially assault Harumin to break her composure but the untimely arrival of her mom put an end to that plan. And finally, their discussion at the end led to both of them blushing at the other words before the big damn kiss. I don't think neither of them has blushed like that in the past.