From Aerandria Scans:

This is a remarkably well-told story about a young woman named Rin, who used to be bullied in high school; and Sayaka, her classmate who used to take half-hearted pity on her. But Sayaka turns out to be a real wolf in sheep’s skin, so when the two women meet again in university at a party, Rin swears to take revenge on Sayaka. The points of view of both Rin and Sayaka are developed equally well and their thoughts and actions make us think deeper about our own conduct towards others.