In this world, magic essence, magic power, magic, and monsters exist. The Demon King appeared in this world. This world has titles, ranked strongest to weakest: Z, X, U, V, S, A, B, C, D, E. To defeat the Demon King, the top five title holders gathered: one title Z, one title X, two title V, and one title S. The title Z holder is you. These five headed to the Demon King's castle. On the way, a blinding light attacked their eyes, and the five lost consciousness. When they came to, they were in a dungeon. The five realized from a wall in the dungeon depicting strange people that this dungeon was said to be nearly impossible to escape. They had no idea what lay within this dungeon.