HOLYYYYY
I can't express enough how peak this adaptation is, we are still at the pretty mundane and slow prologue section of the story, but the manga format sells the story so well, its somehow much better than I remember, this mangaka really rocks and clearly loves the source material, the expressions and paneling and whatnot really stands out for me, who reads so many other mangas and mid adaptations, but maybe its just my bias talking heh.
Come to think of it, yeah, usually novel adaptations are snooze fests full of yapping and walls of text, but with Shuukura, it's mostly the spicy interactions and monologue in their heads, which can be cut down or rather, expressed though the drawing of their expressions. This lends itself really well for manga or anime 😮
Have I missed something, but why is Miyagi being such an asshole?
You missed the part about Miyagi buying her own classmate to do kinky stuff for her. You can infer from this she isn't exactly normal adjusted girl, she disliked Sendai enjoying licking her, but liked when she licked Sendaí's finger and Sendai was put off by it. To explain it fully I'd need to do a whole lot of spoiling and wall text yapping, but basicaly, the short version is,
she enjoys when Sendai is at certain "distance" from her, emotionally speaking, basically the whole novel revolves around this. (light general spoiler)