Sou Akiyama helps organize the Astronomy Club's last cultural festival at Uchihama Academy before the old clubhouse building comes down, just as strange incidents start plaguing its condemned halls. The disturbances intensify soon after first-year Yui Furukawa transfers in partway through the autumn term, pulling Sou into a string of events tied to her arrival that neither of them can explain. Both quickly realize the mystery is bound up with the building's last days.