The story takes place on the Japanese island of Shikoku, in the fictional city of Sanshu, which is based on the real-life city of Kan'onji in Kagawa Prefecture,[3] in the 300th year of the Era of the Gods (, Shinseiki).[4] Yna, Mimori, F, and Itsuki are all members of the Sanshu Middle School Hero Club (, Sansh Chgaku Ysha-bu). The members of the Hero Club are unexpectedly taken to a strange forest by an explosion of light, where they battle enigmatic monsters known as Vertex who attempt to destroy the Shinju (, "Divine Tree"), the guardian god that protects and blesses humanity. Yuna used a special phone application provided by Taisha, a Shinju-related group.