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It's been seven years since Nonoka Komiya last lived in Lake Kiriya City. However, while she knew that there would be changes in the town, she's still unprepared for what she finds upon her return: A giant saucer hovers over the entire city, as it has since shortly after she and her family left. Stranger yet, a girl she doesn't know, Noel, is waiting for her, claiming that they have met before. Confused, Nonaka tries to focus on reconnecting with her old friends, but odd memories, suppressed in the wake of her mother's death, begin to float to the top of her consciousness. Can it be that she has met Noel before? And how does this connect with the appearance of the saucer itself? To solve the riddle, Nonoka must join with her friends and rediscover the events that occurred before she left Lake Kiriya. Because there's more than a mystery that must be solved: there's a promise that has to be kept in CELESTIAL METHOD.