Yuuki Yuuna wa Yuusha-bu Shozoku 3

The story takes place in the era of the gods, year 300. Yuuna Yuuki lives an ordinary life as a second year middle school student, but she's also a member of the "Hero Club," where club activities involve dealing with a mysterious being called "Vertex."
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Aired along side Yuuki Yuuna wa Yuusha de Aru: Washio Sumi no Shou Movie 3 - Yakusoku.
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(Source: Anime News Network)