The Material Defender is Jesus
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Specifically, the game depicts the Harrowing of Hell as described in Dante's Inferno, when freshly dead Jesus goes on a Roaring Rampage of Revenge through Hell, smashing the place up and gathering up the souls of the righteous to take them to Heaven where they belong. The various mines are circles of Hell, the robots are lesser demons, the boss robots are demon princes, and the human hostages are the aforementioned righteous souls. Still not convinced? The first level of Descent II is called "Ahayweh Gate." Abandon Hope All Ye Who Enter Here. Sound familiar?.