Rui was aware of the existence of the underworld and the mafia, however, he did not know that they were such a significant force in the Kandrian Empire. In hindsight, he should have known given the fact that it was almost human nature.
He could see why the Martial Union disliked the Underworld. The Martial Union spent a lot of capital and resources on the sixteen Martial Academies that rigorously trained Martial Artists in hopes that each generation would join and empower the Martial Union. It must be a sore sight to see the Underworld reel in a minority of its investments for its own use.
The unfortunate fact of the matter was that one could probably make more wealth through the Underworld, although there was a huge slew of detriments to doing that.