In the story of Cut Above The Rest the other supporting OCs are usually in one big group or seen one or two at a time. Some of the OCs are closer to others while not being close to Treble, Sparkjump is an example of this. He's there but he's not close to the main character.

So, this is a list of the close friendships in CATR, feel free to add you own in the comments.

Hack and Casino
Oceanic and Sparkjump
Onyx and Treble
Eclipse and Silver
Hack and Treble
Casino and Silver
Onyx and Oceanic
Bass and Oceanic

Well Silver's best friends are: Eclipse, Oceanic, Treble and Casino.