Located on Blue Island, the Manifestation Engine has served as the solution to the world's energy crisis for five years. On the adjacent island of Izu Ooshima live the upbeat Akane Isshiki, her reliable younger sister Momo, and her grandfather Kenjirou, who is one of the inventors of the Manifestation Engine. While they live peacefully beside this powerful creation, everything appears dreamlike until mysterious beings called the "Alone" emerge, aiming to destroy it. After military forces fail to repel the invaders, Kenjirou gives Akane a special key housing the "Vivid System," which empowers her to combat the Alone. Accompanied by Aoi Futaba, Wakaba Saegusa, and Himawari Shinomiya, Akane and her friends unite in the fight against this unexpected enemy, standing as humanity's last hope.