Yuuki Yuuna wa Yuusha de Aru

Yuuna Yuuki spends her school days in the Hero Club, helping people with small problems because she believes being a hero means making others smile. That idea changes when a mysterious system summons Yuuna, Mimori, Fuu, and Itsuki to fight creatures called Vertexes that are trying to reach the divine tree protecting their world.

The girls transform and gain extraordinary powers, successfully pushing the attacks back, but those powers carry a price they were never properly told about. Between classes, club activities, and battles, Yuuna and her friends begin discovering that protecting the world may demand far more than courage, and that the system which chose them does not tell its heroes the whole truth.