Mona, the not-so-slightly narcissistic "queen bee" of her high school cannot stand the fact that the new transfer student, Medaka is not swooning over her like everyone else. So she decides to make him fall for her, no matter what. Obviously, since this is a romance manga, she ends up falling for him first instead, but her motivation (at least as far as she'll admit) remains nothing more than to satisfy her own ego.
Medaka, on the other hand is not immune to her charms because he's dense, like so many other male leads. He's not even immune at all, he's just holding himself back - he is training to be a monk, and that means he is forbidden from having romantic relationships. As far as we can tell, he's choosing that lifestyle of his own free will.
Of course Mona does not know this, but it's doubtful that she'd care even if she did. No matter how many times Medaka tells her that he doesn't want to hang out with her, she doesn't back off - and her attempts at seduction can get rather physical at times. But wait, that's not all! Medaka's classmates actually chew him out for being "mean" towards their beloved idol, and force him to at least be on friendly terms with her whether he wants to or not.
While the manga is rather self-conscious about Mona's narcissism and less-than-pure motives, she still gets away with pretty much anything - and the more I read, the more that bothered me, because, let's face it, what she's doing is basically textbook sexual harassment. But she's a girl, so it's apparently okay. Yaaay.
