Kurumada Suikoden Hero of Heroes

The Mythology is the plan of the gods. A perfect story created by them, that should never be changed in any way. However, there where mortals who altered the Mythology with their own hands. Pegasus Seiya, Ryuji Takane, Kojiro of the Fuuma, and many others were brought to this prison, where they're going to be erased to restore the Mythology to its original course... But they're not going to disappear without fighting for their existence.