Yue is the other bookworm of the class of 31 (the first being Nodoka). Seeing her friend, the shy Nodoka, get a crush on Negi-sensei, she does all she can to push her forwards. She is a member of the Baka Rangers (she's Baka Black), so called because there are 5 girls who consistently do badly in tests. However, Yue has a highly intellectual brain - it's just that schoolwork holds no interest for her and she doesn't see why she should put in the hours to learn such boring knowledge. She is also a member of the Library Exploration Club (see Nodoka's bio for what this club is) and has a taste for strange, obscure juices. At first, she seems to be one of those deadpan charas (though not to Ayanami Rei levels) who speak with a level-toned voice. But actually, she's fairly easy to rile up under the right circumstances where she will bubble with delicious emotion.
Incidentally, Akamatsu-sensei has admitted that she is a homage to Patchouli Knowledge of Touhou.