The story takes place on the Japanese island Shikoku in the fictional city of Sanshu, based on the real-life city of Kan'onji in Kagawa Prefecture,[in the 300th year of the Era of the Gods Yuna, Mimori, Fu, and Itsuki are all members of the Sanshu Middle School Hero Club Sanshu Chugaku Yusha-bu), dedicating themselves to helping those that request help. One day in their regular daily lives, the Hero Club members are suddenly caught in an explosion of light and transported to a strange forest, where they encounter mysterious monsters known as Vertex which seek to destroy the Shinju ("Divine Tree"), the guardian deity which protects and blesses humanity. Using a special phone application granted by Taisha, an organization dedicated to the Shinju, Yuna and her friends must transform into "heroes" with magical powers to protect their world from imminent destruction.