In the 29th year of the Divine Era, a generation after Japan was ravaged by a celestial beast, leaving only Shikoku untouched, young ones dwell in harmony within the protective walls shielding Shikoku. Amidst this tranquil era, a girl named Yuuna, bearing a namesake commemorating a fallen hero, stands out. Despite her namesake's valorous connotations, Yuzuki Yuuna lacks any extraordinary abilities. Discovering another Yuuna at her school, Fuyou Lilienthal Yuuna, who harbors a fervent desire to venture beyond the wall and witness the world's true nature.