Story
Gunjo Gakuen (Deep Blue School) is a facility designed to gather and isolate those students with a high adaptation coefficient (indicating that the student is less likely to be able to adapt to society), determined from an adaptation exam mandated by the government.

After a failed summer vacation with other members of the school's broadcasting club, Taichi Kurosu and some of the other club members return to the city, only to find that all living creatures within it except for the club members have completely vanished. In order to confirm the status of the outside world, Taichi decides to gather other club members to help Misato Miyasumi, the president of the broadcasting club, set up a broadcasting antenna to contact any possible survivors. However, Taichi soon discovers that the world is actually repeating the same week and thus all their actions are reset, with no loss or gain, no matter what actions are taken. Seeking himself and the restoration of broken bonds, Taichi must discover meaning to exist in this strange and lonely but, for Taichi, comforting world.

Taken from Wikipedia