From ShoujoMagic:
Ryou has the biggest breasts of any shoujo manga heroine to date! But life isn't any piece of (cheese) cake, because she's constantly being assaulted by perverts who want to cop a feel. The first man who doesn't obsess over her assets turns out to be the first man she ever wants to have obsess over her, though there's something strange about him... One time she's with him, he's a sweet masochist, the next time he's a bold sadist. Which does Ryou like better? The S or the M? She'll have to make a choice, because it turns out that she CAN'T have both. Find out the surprising reason why one face has two personalities!!