A school frozen in time

It is a cold winter morning, seemingly like any other, when a group of students notice something amiss—the entirety of Seinan Gakuin High School is empty. There is nobody else in the building aside from eight third-year students: Takano, Mizuki, Sugawara, Rika, Shimizu, Mitsuru, Akihiko, and Keiko. No one is able to leave the school or contact anyone outside, and everyone's watches are stopped at 5:53, as if the school is frozen in time. Soon, a startling realization about the nature of their predicament strikes the whole group: this is the exact time a student had fallen off the building sometime ago. Even more terrifying is that no one can remember who the student was. Not long after, they all spot a mysterious "Do you remember?" message on their homeroom chalkboard. The person who committed suicide, the eight students with altered memories, and the ominous circumstances of the school—can all these distinct events somehow be related?