Hensuki

Plot
Hensuki revolves around Keiki Kiryū, an ordinary high school student who finds an anonymous love letter addressed to him. What makes things even more interesting is that attached to the letter, there's a pair of panties. To determine the identity of his secret admirer, referred to as "Cinderella", Keiki proceeds to investigate several possible candidates, including: his senior and president of the calligraphy club Sayuki Tokihara; his underclassman and assistant librarian Yuika Koga; and his classmate and close friend Mao Nanjō. However, as Keiki seeks to uncover who this mysterious girl might be, he discovers that every girl he suspects is singularly perverted and desperately interested in getting him to participate in their perversion.