After Chapter three, the Jail Tower area will open up. While it's clearly intended to be an endgame dungeon, you can exploit it for items and weapons. Enter when your Libido gauge is near full and save near an item spawn point. Select the Merchant Encounter Up on the roulette wheel and then walk around until he appears. The weapons, items, and armor he sells will all be endgame or near endgame quality. While expensive, even a single weapon can turn a Blood Maiden into an engine of destruction.