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.'(Source: ANN)Aired along side Yuuki Yuuna wa Yuusha de Aru: Washio Sumi no Shou Movie 3 - Yakusoku.