Hmmm, its not that they're *side* characters but that they're introduced later in the series.... its more the case that the main 4 drop back a bit while the new ones are on stage and that the permutations of social nets increase.
I figured we'd see about 10 episodes of the '4 musketeers' and then we'd start seeing the others appear and watch the exploration of the net of friendships expand. I hate to note this but: