Personality. Due to being bullied for years and never making any friends until meeting Sonic, Nine is bitter and much more snarky, antisocial and short-tempered than most versions of Tails. And while he's gained independence, he's also very jaded, and only goes against the Chaos Council to stay with Sonic. He has an extra tail, as a fox he was bullied, as the years pass by, he made himself to have these 8 robotic tails, using his intelligence in doing so.