Yuki Yuna is a Hero

Members of the Hero Club at their middle school are chosen by a divine system to become magical girls and protect the world from mysterious entities called Vertex. Cheerful and determined Yuki Yuna leads her friends into battle with unwavering optimism, but they soon discover the system exacts a terrible and permanent price for the power they use. The series builds a deceptively warm atmosphere before revealing a deeply tragic truth about their situation.