Precocious kid, but I'm surprised he got through Apollo's shell. Half-expecting he's playing Apollo like a fiddle, but it was fun reading the interaction between the two. Cario definitely doesn't act like I expected, but he's consistent and believable. It's a small detail, but I appreciate that he didn't go into a sob story -- that is a trope that I see abused all too often.
One thing I would recommend is setting the scene at the start of a chapter. It took some time to work out where everything was happening, and even a sentence or two saying they're on the street outside GUNSMITH can keep the reader's focus on what's happening instead of hunting for clues about where everything is.