The Melancholy of Haruhi Suzumiya Season 1 episode 17 (2009)

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Like the previous episode, Kyon's easy going summer vacation is interrupted as the group is taken on a whirlwind tour of summer activities, from swimming pools to summer festivals, part-time jobs, and stargazing. However, Kyon is wracked by a constant sense of déjà vu. Koizumi is likewise troubled, while Nagato seems even more detached than usual. They finally work out the truth: Haruhi has put the last two weeks of August into an infinite loop because she refuses to let summer end. They find out that the loop has repeated 15498 times. However, none of them can devise anything to stop the cycle from repeating. On the second-to-last day of summer, Kyon calls out after Haruhi in a last-ditch attempt to stop her from leaving unsatisfied, but fails to think of anything he can do, and she leaves. As the last day of vacation arrives, Kyon, resigned to the loop repeating itself, goes to bed without finishing his summer homework.