Rico is a classic street urchin, a homeless young boy who lives on the streets of Venice, especially the Outer City. He feeds himself by running errands for anyone who can spare a few coins.
It seems the Backstreets rogue Rat is one of his occasional clients, even though the rogue often beats him.
Rico can provide only limited information about the city, though he knows Nox does a lot of strange work with books in the Backstreets. He likes sweets.
If Scarlett threatens Rico or otherwise gets on his bad side, he will refuse to speak further with her. That's only an issue if Scarlett wishes to learn rogue Physical Skills from Crowe, since she'll have to complete A Rat's Work quest to get an introduction. To get Rico wiling to speak with her again, offer him sweets (if Scarlett doesn't have any sweets, she can buy them at Madame Orlof's bread stand in the Outer City Marketplace.