...... did this get lewder?
This is just repeating a point that I’ve made before, but I really do think this series is notable for the fact that its fairly considerable lewdness is almost entirely conceptual rather than visual—while it occasionally skirts the edges of visual ecchi (like with Koguma and Omichi in their little sub outfits), it scrupulously avoids the standard gratuitous ecchi upskirt and sideboob, etc. shots.
Also as has been mentioned before, a weirdly parallel series, albeit with a much more aware “good girl” protagonist, a more overtly perverted delinquent, and much more forthright sexual content is Yuugai Shitei Doukyuusei (“Harmful Designated Classmate”), with a new chapter available on Mangadex. The basic character dynamic is not at all dissimilar, though.