In the near-future, the world's energy problems have been solved thanks to a scientific power known as the Manifestation Engine which provides energy from the sky. On the island of Izu Oshima, Akane Isshiki is living a simple life with her sister, Momo, and her grandfather and creator of the engine, Kenjirou. As Akane eagerly awaits the arrival of her classmate, Aoi Futaba, who is traveling to the nearby Blue Island for treatment, she and Momo hear an explosion coming from their home and discover that Kenjirou has somehow switched bodies with a stuffed otter doll as the result of an experiment. Undeterred by his new form, Kenjirou gives Akane his latest invention, a strange key known as the Operation Key. She is informed that this is the key to accessing the Vivid System, which is the only thing that can fight against an alien race known as the Alone. Meanwhile, an Alone (Four Legged) is seen attacking Blue Island, where the Manifestation Engine is stored. As Aoi's transport is hit and crash lands on a ledge, Akane and Kenjirou rush to their location, but Akane is soon struck by her fear of heights that she gained during a traumatic incident seven years. When Aoi starts to fall towards the sea, Akane overcomes her fear and dives after her. Her key soon glows and she is able to activate the Vivid System, granting her a suit called the Pallet Suit which keeps her and Aoi from falling. Kenjirou explains that this system is for Akane and Aoi to fight against the Alone.