The main characters are Stiles and the Cullens. Stiles is known for his ability to adapt in strange situations. When he meets the Cullens, their interactions will be centered around how they deal with each other's differences. The Cullens' vampiric abilities and Stiles' human (or whatever he is in his original context) nature will play a big part in their relationships in the fanfiction.
Obviously, Naruto from the Naruto series and the Cullens from the Twilight series are the main characters. Naruto is a young ninja with big dreams and lots of energy. The Cullens are a family of vampires, each with their own distinct personalities like Edward who is brooding and Bella who is strong - willed in her own way.
Obviously, Bella and the Cullens are the main characters. Bella is the human girl who enters their world. And the Cullens include Edward, who has a special connection with Bella. Then there's Alice, who might be able to see the future and could play an important role in Bella's interactions with the family. And of course, Carlisle, the head of the Cullen family.
In this fanfiction, Stiles might initially be in awe of the Cullens' beauty and grace. Maybe he'll be a bit intimidated by their vampiric nature at first. For example, he could be shocked by their superhuman speed or strength when he first witnesses it.
Stiles is the key character here. He's the one through whose perspective we usually experience the story. In the pack, Scott is a must - he's the werewolf who has a long - standing friendship with Stiles. Derek, with his alpha - like presence, also plays a major role. Additionally, characters like Allison, who has her own arc related to the supernatural world, could be part of the main cast as well. They all interact with Stiles in different ways when he meets the pack.
There could also be other characters from either Stiles' world or the Winchesters' world that make appearances. For example, in Stiles' world, there might be his friends like Scott who could be mentioned or even play a small part in the story. And from the Winchesters' side, characters like Castiel could potentially show up and interact with Stiles in some really interesting ways.
Obviously, Bella and the Cullens are the main characters. Bella is the human who enters the world of the Cullens. And the Cullens include Edward, who has his own complex personality and abilities as a vampire. Then there's Alice, who might be able to see the future and plays an important role in Bella's interactions with the family.
Obviously, Stiles and members of the Hale family are the main characters. Stiles, with his quick thinking and sarcastic humor. And the Hale family members, like Derek Hale, who is often portrayed as brooding and strong, and other family members with their own unique personalities and supernatural abilities.
Edward is also a fascinating character. His struggle with his vampire nature and his growing feelings for Bella can be explored in more depth in the fanfiction. Maybe we'll see new aspects of his character, like his relationship with his vampire siblings in the context of Bella being in their lives.
The Cullens themselves are the main characters. There's Carlisle, the patriarch of the family, who as a human now has to use his medical knowledge in a new way. Esme, who might be exploring her newfound humanity with a sense of wonder. And then there are the younger Cullens like Edward, Bella (if she's involved in this particular fanfiction), and the others, each having their own unique experiences and reactions to becoming human.
Stiles is a must - have main character. Then, depending on the direction of the fanfiction, characters like Simon Lewis could be important. Since Simon is a vampire in the Shadowhunter universe, his interactions with Stiles, who is new to this world, could be really interesting. Also, characters like Luke Garroway, the werewolf, might play a role, especially if the story involves the relationships between different Downworlder groups and Stiles' place in all of that.