Atsuko Yoshikawa attends the prestigious Siren Academy, a boarding school for girls. She harbors a secret romantic relationship with Sayaka Matsumoto, a bond formed during their high school years and concealed from Atsuko's older sister. At the academy, Atsuko shines as a lacrosse star, her athletic prowess fueling her popularity among the student body. This very popularity sparks tension with Sayaka, who displays possessiveness and craves Atsuko's exclusive attention. Their interactions within the school dormitory include intimate moments sometimes disrupted by other students. The academy itself exists amidst supernatural threats, including entities connected to Professor Goda's activities.