Gokukan Ryoujoku ~Zetsubou Animation Koku~

Kiriya Ren is the president of the student council in a private school.
Everybody loves and admires her. However, with the appearance of the
genius transfer student Sawada Ria, her school life drastically changes.

Though all she ever wanted was to live in peace, Ren finds herself fallen from grace.
She loses her position as well as her lover, and she swears she will take revenge.
She succeeds in capturing and imprisoning Ria, after which she begins her cruel abuse.

[From DLSite English]