Most likely the general himself is a main character. Since it's a story about him, he would be central to the plot.
I'm not sure specifically as I haven't read it directly. But generally, it might be about a general in the context of the Big Valley. It could involve his adventures, his relationships, or his contributions in that particular setting.
There are many possibilities for the main characters. It could be the valley's caretakers, if there are any, whose job is to maintain the balance in the valley. Or it could be a group of scientists who are studying the ecological system of the big valley. Another option could be a young couple who fall in love in the beautiful and mysterious big valley.
Often, the early settlers are main characters. They are the ones who started everything in the valley.
The main character is, of course, the star general. He is the central figure around which the story revolves.
Since it's not clear what these stories are exactly, the characters could be anyone. Maybe local farmers, ranchers, or adventurers in the big valley.
As I haven't read it, I can't say for sure who the main characters are. But I assume there would be the girl herself, and perhaps her friends or family members who play important roles in her story.
Obviously, Big Bruda is one of the main characters. He is usually the central figure around which the story revolves. There might also be side characters like his little sister, who often looks up to him, or his best friend who accompanies him on his adventures.
It could also feature some new or original characters created specifically for this fanfic. These new characters might play important roles within the 'pack', bringing in fresh dynamics. For example, a new ninja from a different village who has a special ability that is crucial to the 'pack's' survival or success.
The main characters would surely be Naruto and Sasuke. Their final battle at the Valley of the End is a crucial part of the Naruto story. However, in a fanfic, characters like Itachi could also be brought in. His influence on Sasuke and his actions in the overall Naruto plot could be explored in relation to the Valley. And don't forget about Jiraiya. His teachings to Naruto could be revisited and related to Naruto's experiences in the Valley of the End.
A vampire from the Twilight world could be a main character. Maybe he's tired of the city life and the constant power struggles among his kind. So he travels to Bear Valley Ranch, attracted by its isolation. And there, he meets a local girl who is not afraid of him and they form an unlikely friendship. There could also be an old wise man on the ranch who has known about the Twilight secrets for a long time and serves as a guide to the others.