Karasu is a local to Prospect, perhaps they met sometime ago before he went to Japan or knew each other when growing up?
Imports/Exports
Karasu has taken over the family business and is now attempting to pick things up from how his family had it.
Entrepreneur
Karasu likes to be part of business, and is often looking to help either promote local business or be part of it, example, taking up part owner-ship of the Kokuren Kyabakura once Ogami Itto resigned.
Occult
Karasu is known to frequent strange places and cults, not sure if he is part of any, but who knows!