Mysterious destructive forces called Vertexes begin threatening the world Yuuna Yuuki loves, and the Hero Club is called upon by a strange phone app to save it. Along with her best friend Mimori, as well as sisters Fuu and Itsuki, they must transform into magical girls in order to battle the Vertexes. Yuuna and the Hero Club must fight for the very existence of their world and face the harsh truths behind their own powers, all the while discovering what it truly means to be a hero. (myanimelist)