We came from the far future, where most of the adults have disappeared as if they vanished into thin air and all of the children are managed by a few adults. To discover the cause behind human extinction and to evade it from that root cause... That's what we had jumped to the past for, supposedly. 
A boy sitting in the seats of a movie theater fidgets with his cellphone. "Before aptitude or anything, trying to change the future with just five kids? You would think there's a limit to lack of planning," he typed on his cellphone. 
The boys wonder if they had really come to the past. Why? Because, ever since they arrived, they haven't stepped one foot outside this theater.

"A classmate still remaining here is the cause of human extinction." 
That's what it said in the letter from the past, written in the familiar handwriting of my friend. The next day, I decided to go to school, though I can't remember how many weeks it's been since I last went. 'I decided to go search for the culprit' would be a lie, but 'it didn't matter' would also be a lie. 
"Hey Arata, I almost thought you'd forgotten how to come to school." 
Oh, &#12450;&#12521;&#12479; (Arata) refers to me by the way. It's written as &#26032; in kanji. The kanji is often misread as &#12471;&#12531; (Shin) though. 
"Huh, and what'd you come here for Nouko? Come here often?" 
The students here are what you would call 'the losers'. At least, from the perspective of time travel, they are all classified as useless. I am also one of them.

Four high school girls in uniforms walk silently on the barren earth. These girls are time travelers who had been sent 6000 years into the future, from their present in which the same day is endlessly repeated, in order to evade human extinction. 
They studied time travel in school, were examined by the aptitude test, and were sent to the future as told. What should they do now? They had no idea. The only thing they could take with them from the present was a light, toy-like cellphone. Of course, it receives no signal here. 
As the girls are walking, they see strange birds flying in the sky, and a discolored river in the distance. 
Then, one girl finds an abandoned house, and recognizes the name inscribed on the front gates.

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