In order to save his younger sister who has fallen from a curse, Gideon decides that he must enter the 'Prison Dungeon' in order to retrieve the one item that could save her.

Along the way, he will have to face vicious monsters that have been enhanced by an unknown lifeform, and the evil criminals who were thrown into this prison world.

This is a story of a young man who challenges such an overpowering world alone, a heroic tale of sacrifice and salvation.