There's no anime arc as infamous as The Melancholy of Haruhi Suzumiya's Endless Eight. Midway through the anime's second season, Haruhi Suzumiya gets unknowingly trapped by the SOS Brigade in an unbreakable time loop that forces them to repeatedly experience the best week of summer 15,532 times. The loop only gets broken when Kyon remembers to do his math homework and deduces that all Haruhi has wanted is to spend as much time as possible with her friends.
Source：https://www.cbr.com/haruhi-suzumiya-endless-eight-arc-anime-genius/
