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失われた未来を求めて
Kaori Sasaki—a member of Uchihama Academy's Astronomy Club—confesses to Sou Akiyama, but later that evening, she dies in a tragic road accident. Her friends and fellow club members mourn her death in a local hospital. Yet she shows up to school the following day, and no one senses anything amiss. The day finishes without any unusual incidents, and the group of friends plans for the upcoming cultural festival. Suddenly, the room is shaken by an unnatural earthquake. Everyone splits up to investigate—except for Nagisa Hanamiya, who stays behind. As everyone leaves, Nagisa notices that the odd relic-like cube that she was toying with starts emitting a strange blue light. Meanwhile, Sou stumbles upon an unconscious, naked girl lying in a pool of water.
Sou is an ordinary high school student. His biggest worries are his Astronomy Club's project, the zany antics of his fellow club members, and his childhood friend who's suddenly not her usual cheerful self. But then, things take a strange turn...
After Yui's sudden and mysterious appearance, the Astronomy Club gang tries to make her feel welcome as she struggles to figure out what she is doing at Uchihama Academy.
Airi reminisces about how she met Kaori and Sou. The Astronomy Club once again takes on the Judo and Karate Club dispute, with a slightly different outcome. And they also make headway on the case of the school ghost.
Sou enjoys getting to know his new camera. And to give Sou more quality time with it, the Astronomy Club uses the fine weather as an excuse to skip classes to go for a picnic. But things go slightly awry when they miss their bus stop.
The kids yawn through a lecture on quantum theory and Schrödinger's cat. And after classes, the Astronomy Club gets to the bottom of the oddly low-tech school festival project of the Computer Club.
The Astronomy Club members discuss the career paths everyone plans to take after high school. But Sou finds out that Nagisa's path is further complicated by an arranged marriage looming over her head.
The Astronomy Club preps for the school festival, half of them working on the planetarium and half of them working on the café side of things. And Yui's apparent concern for Kaori leads her to do some odd things.
As the fateful day of Kaori's accident approaches once more, everything plays out slightly differently due to Yui's presence.
Kaori's poor prognosis of recovery from the accident leaves everyone reeling and desperate to find some way to save her.
Yui returns to her save point once more and she recalls all the things she has tried before, each time hoping for a different outcome.
Things are going quite a bit more differently in this timeline as Sou's interest in Yui seems stronger than usual. But even as the outcome remains uncertain, Yui ponders what the consequences will be if she succeeds.
Yui succeeds in keeping Kaori away from the accident and disappears, almost as though she never existed, but the other members of the Astronomy Club are left with a nagging feeling that they are missing something.
