Basically 200 pages of people making increasingly emotionally immature decisions.
Between the Sheets (Sheets no Sukima) is actually pretty good at depicting how idiotically people can behave when love & lust are involved. Basically none of the four major characters make any really good decisions over the course of the book, and their motivations are a mix of lust, envy, and spite. A little painful and a little cringeworthy, though mostly because you know you’ve seen at least some of this play out IRL.
That said, the back-cover claims that “Erika Sakurazawa boldly introduces a new type of relationships for girls” and I can only pray that
the Minako/Saki dynamic is no reader’s first romantic rodeo. Minako has a romantic crush on her best friend Saki (who by all accounts is pretty solidly heterosexual), causing Mina to go through various stages of angst, sorrow, anger, and scheming. Unless by “new type of relationships” they meant “toxic ones”, in which case, Between the Sheets is perfect.
Nobody in this book is coping healthily with anything, be ye warned.