Obviously, Naruto is often a main character. Since it's about the Ten - Tails in the Naruto universe, he's usually at the center of the story, whether he's trying to defeat it, control it, or understand it.
The Ten - Tails itself can be considered a main character in a sense. In fanfiction, it can be given more personality and motives. It's not just a mindless force of destruction but a complex entity that interacts with Naruto and other characters, driving the plot forward.
The main character is of course Tails. He's the center of the story in Tails Christmas fanfiction. However, Sonic is almost always around. They're a duo, and Sonic's adventurous spirit adds to the Christmas story. Amy Rose is another character that often shows up. She's into girly things like making Christmas cards and planning parties. Then there's Big the Cat. He might be fishing in an icy pond for a special Christmas dinner ingredient. And don't forget about Rouge the Bat. She could be looking for some valuable Christmas - themed treasure.
In 'baby tails sonic fanfiction', the two main characters are, without a doubt, Baby Tails and Sonic. Baby Tails is often portrayed as an innocent and curious character. Sonic, on the other hand, is the more experienced and heroic figure. They are the core around which the story revolves. However, we may also see the appearance of other Sonic characters like Cream the Rabbit or Rouge the Bat in some fanfictions, but their roles are usually secondary compared to Baby Tails and Sonic.
In addition to Naruto, other characters like Sasuke could also be main characters in this type of fanfiction. Sasuke has always had a complex relationship with Naruto and the power of the Ten - Tails could bring new challenges and opportunities for their relationship. Also, characters like Kakashi who are important in Naruto's life might also play significant roles.
Naruto himself is often a main character. Since he has a strong connection to the tailed beasts in the original series, in fanfiction involving the Ten Tails, he is usually at the center of the action, trying to either defeat it or understand it better.
There could also be the villains. Depending on the context of the fanfiction, it might be Dr. Eggman. He's always trying to cause trouble for Sonic and his friends, and he could be the one behind the situation where Tails almost dies. So Dr. Eggman would be a main character on the opposing side.
The main characters are often Naruto, as he is the focus of the mecha concept. Shikamaru could also be a main character in this type of fanfiction. He would be the strategist, trying to figure out how to best utilize the mecha Naruto in battles. Additionally, Orochimaru might be a character in some cases. He could be interested in stealing the technology of the mecha for his own evil purposes or trying to manipulate Naruto through it.
Obviously, Naruto is the main character as the story focuses on his growth of the nine tails. Kakashi could also be an important character. He might be the one guiding Naruto in controlling his new power, given his experience and knowledge. Sakura could play a role too, perhaps as a healer in case Naruto gets injured during his power - growth process.
The main character is Naruto for sure. But other characters like Jiraiya might play a significant role. Jiraiya could be the one to guide Naruto in controlling the four - tails' power. Also, characters from the Akatsuki might be main antagonists. They would be interested in Naruto's new power and try to capture or use him for their own purposes, like Pain or Itachi.
Sometimes, other characters from the Naruto universe might also play important roles in these fanfictions. For example, Kakashi could be involved as Naruto's mentor, giving advice on how to better communicate with the Nine - Tails. Or Sakura might be there to support Naruto in his journey of befriending the Nine - Tails, even if she doesn't directly interact with the tailed beast.
Obviously, Naruto and Matsuri are main characters. Naruto, with his energetic and determined personality, often drives the story forward. Matsuri, being from Suna, brings a different perspective to the story. Sometimes, other characters like Sakura or Kakashi might also make an appearance to add more depth to the plot.