I can convert prisoners into Netherworld Citizens. There are multiple quests that ask you to add them. But nothing explains what their purpose actually is. It just says they give several benefits.

2 Answers

Making them citizens doesn't appear to do anything useful beyond side quests and the trophy for making 100 prisoners citizens.

The sidequest name is what tells you what making citizens does, quest is called boost pop , items and weapons have a pop limit the amount of innocents it can hold. so making citizen increases your interrogators (random item equipped by them) innocent pop cap higher.

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