Demon's Tier+

Villagers sit in cages on levels 2, 5 and 9. To get it you need to find and open all three cells in one playthrough. To open the cage you need a silver key. Keys very rarely drop from "hidden" monsters, and can also be bought at the store in the city. I recommend purchasing keys as soon as possible, since residents give money when returning to the city, which more than covers the cost of purchasing keys.