Yukari is a "bad girl." She rebels against her controlling mother by dyeing her hair, polishing her nails and having an older boyfriend, with whom she has an intimate relationship. In fact, as she notes, that's kind of all they have right now. He never takes her anywhere; they just go to a karaoke box, sing a bit, and have sex.
Miki is a "good girl." She's tall, and has classic Japanese beauty. She's quiet and bookish and smart. And a bit aloof.
The two are forced to share a double desk at the beginning of the term which annoys Yukari to no end. Like most bad girls, her initial reaction is disdain and derision for the good girl's behavior. But, one day, after school, she sees Miki in the Art Room, gently kissing a statue of Mars and her heart starts to race. When someone comes up from behind, both Miki and Yukari know that they've been seen, and everything changes between them.