Its bug, it wont show unless i click on the error message on the screen and when 
I defeated it but it wont let me finish the quest.
Viewing post in The Exiled Demon Prince comments
Hmm...when did you download the game? 3 days ago I uploaded a patched version that addressed this and a few other issues.
As for the bounties, the entire adventurer's guild is in an experimental state right now(it will be fully functional in the next update). I didn't expect so many people to continue playing even after unlocking every scene in this version