Towards the Eternal Night...

July 20, 1999, the end of the first semester, with summer vacation starting tomorrow. Arita, a high school teacher, suddenly finds herself repeating the same day over and over again. After looping for the umpteenth time, it turns out that the beautiful teacher, Masamune, and the brilliant student, Gagawa, who is ranked first in his grade, are also in the same situation. On the morning of the last day of school, they are trapped in a time-space of only a little over three hours after the warning bell. As Arita investigates, he finds others who are also aware of the loop, and they begin to close in on this grand mystery. Will they be able to escape from this eternal time and grasp tomorrow?