Yuuki Yuuna wa Yuusha-bu Shozoku

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." Includes the special 4koma, Washio Sumi is a Hero: Another Story.

Source: ANN