Thank goodness Rax doesn't show up a lot in this novel, because he's a thoroughly dislikable sort of person. A bully, a gang leader, a snitch, and a jealous idiot who won't have anyone else behaving differently than himself, or being considered more important than himself.
As a result, Rax is the rascal among the new cadets to Arth who eggs on his gang to play pranks on Tod, Josh, and Philo -- some of them very dangerous pranks, including the one that gets Tod in big trouble just before the Celestial Omnibus shows up.
The one bright spot about having to encounter Rax is the certainty that by the end of this novel he's going to end up in deep trouble, while the ones he's been terrorizing will be both rewarded and vindicated. I think it's called "schadenfreude."