Oikura, Sodachi

Sodachi was the president of a first-year class where both Hitagi and Koyomi also belonged to. At school, she wanted to be called as "Euler," but ends up getting the nickname "How Much," a pun on her surname (お幾ら, o-ikura) and a reference to her personality.

Two years before the present time, Sodachi joined a study group before the year's final exams, and later achieved a score of 99/100, making her the second highest-scoring student in the class. However, the unusual results of the math exam among those who attended the group study and those who did not sowed doubts, causing Sodachi to hold a class meeting in order to determine the culprit who had leaked the questions for the exam. The class assembly itself was inconclusive, but Sodachi was pinned as the perpetrator by majority vote.

Despite being experiencing such a fate, Sodachi was able to continue studying, but stayed at home during the two years that followed.

(Source: Bakemonogatari Wiki)