Intelligence, currency, membership fees.
'Black Prison' currently only has these three areas of business, but, of course, these aren't all. New businesses may be added in the future, such as treasure hunting, security, weapons, and so on. However, they aren't needed right now—slow and steady it is.
He plans to make 'Black Prison' a comprehensive force, the main feature of which is that all of its operations will be related to violence and 'slightly' illegal activities. In other words, it's a 'department' specifically for the dirty and tiring deeds.
