"Yuuki Yuuna wa Yuusha de Aru" is a 12-episode anime series set in a world where humanity is protected by a group of young girls known as the Hero Club. These girls are chosen to become "Heroes," individuals granted magical powers by the Shinju, a divine tree that safeguards humanity from the destructive forces known as Vertexes. The story primarily takes place in Sanshu Middle School, where the Hero Club engages in community service and everyday activities, unaware of the true nature of their roles until they are called upon to defend their world.

The protagonist, Yuuki Yuuna, is an optimistic and cheerful member of the Hero Club, joined by her friends: the responsible and level-headed club president Mimori Togo, the energetic and competitive Inubouzaki Fu, and the reserved yet kind Inubouzaki Itsuki. Together, they balance their ordinary school lives with their duties as Heroes, which involve transforming into powerful warriors to combat the Vertexes. These monstrous entities emerge from beyond the Shinju's barrier, threatening to destroy humanity.

As the series progresses, the girls discover the harsh realities of their powers. Using their abilities comes at a cost: each transformation and battle gradually erodes their physical and mental faculties, leading to permanent disabilities such as loss of sight, hearing, or mobility. This revelation adds a layer of tension and emotional weight to their struggles, as they must grapple with the sacrifices required to protect their world. Despite these challenges, the girls remain determined to fulfill their roles, driven by their bond with one another and their desire to safeguard their loved ones.

The narrative explores themes of friendship, sacrifice, and resilience, as the Hero Club faces increasingly difficult battles and personal trials. The climax of the series sees the girls confronting the true nature of the Vertexes and the Shinju, leading to a resolution that tests their resolve and unity. Through their journey, the series examines the balance between hope and despair, as well as the strength found in camaraderie and selflessness.