Following the shocking loss of their beloved professor at Nankai Academy, the four resolute students intensify their search for answers. The discovery of her planner, marked with the names of seven girls on the night of the incident, provides a vital lead that draws them into direct encounters with each one. Through determined questioning and strategic pressure, fragments of information surface that hint at hidden connections. Yet as the investigation lengthens, the students sense their focus shifting under the weight of their own emerging impulses.