Tokihara Sayuki

Japanese name:

朱鷺原 紗雪

Sayuki is a third year student and president of the calligraphy club. She is a hardcore masochist who longs to be Keiki's "pet". She repeatedly uses hidden cameras to gain material with which to blackmail him into satisfying her fetish. She'd known about Yuika's fetish from the first time they met and immediately became fierce rivals, constantly fighting for his attention.

Wikipedia