At a hanshake event for the Pure Idol club, popular idol Karen Amemiya is cut by a male fan with a knife. Half a year later, high school student Nina Kamiyama is the only girl at school who wears the uniform pants instead of a skirt, and is disconnected from her classmates. A teacher then announces that a suspicious person has been going after high school girls recently, and female students should head home in groups. However, Nina ends up leaving alone, and suddenly a figure with a knife appears out of nowhere!