In one world, there reside four heroines. Each of them have powers, they are Aiko Yukami, Veiruno Ventria and Noir Neppa. They are a crucial impact to their society, they protect them from darkness. But one of them, is a mystery.
That mysterious heroine is named as Sakuroi Sphere, her pure appearance is yet unknown, but people know her as the owner of the land, Spheric Metropolis. That metropolis is one of the most richest of the lands, but everything changed.
Where darkness, distortion and pure evil has spread across the lands.
Who caused it? No one knows.