**Mathematics instructor Saki Tachibana maintains a trusted position at Saint Cecilia Girls Academy, an elite institution masking sinister operations concerning the demonic violin Cannone. She leverages this trust to advance headmaster Akio Yashiro's malevolent objectives, directly supporting his dark agenda centered on the chapel-sealed violin—an artifact possessing the power to entrance victims. Official media offers no details regarding her background, motivations, or personal history. Her character undergoes no documented development across the OVAs, and her narrative role remains exclusively dedicated to facilitating the academy's hidden schemes under Yashiro's direction.**