The Devil Inside follows Dave, a man hiding a dark secret: a demonic alter ego named Deva who can surface under the right conditions. Dave is coerced into participating in a brutal reality television show built around monster hunting — audiences must be kept entertained at any cost.
At designated transformation points in each stage, players can switch between Dave's gun-based combat style — laser-sighted firearms and ranged precision — and Deva's supernatural approach, which draws on magic points, lets her float through the air, and allows her to slowly regenerate health by consuming souls from defeated enemies. The dual identity is both Dave's curse and his greatest tactical asset.