There is Minami Shimada, who plays an important role. And then there are other students as well, like Akihisa Yoshii. They are all involved in the baka tests and the various happenings in the school.
Akihisa Yoshii is one of the main characters. He is often considered a bit of a 'baka' but has his own charm. Then there is Minami Shimada, a girl who has a certain relationship with Akihisa. There is also Hideyoshi Kinoshita, who has some unique characteristics.
I don't know specifically as there are many light novels with this name. But often in such light novels, there could be a young protagonist, perhaps a student who is smart but a bit of an oddball. There might also be his or her friends, like a girl who is really good at a certain subject but has a quirky personality.
Since I'm not familiar with this specific light novel, I can't tell you the main characters. But in a lot of light novels, the main characters are usually students or young people. So in 'baka no test light novel', it could be a group of students who are at the center of the story. They might be facing challenges together, and their interactions with each other would form the core of the plot. There could be a leader - like character, a comic relief character, and others who each bring something different to the story.
Yuuji Sakamoto is a popular character. He's known for his laid - back attitude and his ability to come up with unorthodox solutions to the various tests in the story.
From 'Baka and Test', Himeji could be popular in the fanfic. She's smart and cute, and her interactions with the 'Naruto' characters would be interesting. And then there's Sakura from 'Naruto'. Her growth as a character and her skills could make her a favorite in the 'naruto baka and test fanfic' as she tries to navigate the new situations.
One of the main characters is Akihisa Yoshii. He's a bit of an idiot but also very endearing. He often gets into all sorts of comical situations with his classmates. Another important character is Mizuki Himeji. She's a smart and cute girl who has her own role in the various happenings in the school. And of course, there's Minami Kei who is also quite prominent in the story.
I'm afraid I can't name the exact main characters without having read it in detail. But from what I know about similar light novels, there could be a lead character who is somewhat of an underdog. He might be joined by a group of friends with diverse personalities. There could be a tsundere - type girl who is initially cold but warms up over time. And perhaps a nerdy character who is really good at academics but lacks in social skills. These are just speculations based on common character archetypes in light novels.
I'm not entirely sure specifically as it could be a very specific or fan - created 'Test' - related fanfic. 'Baka' means 'fool' or'stupid' in Japanese, so perhaps it has some comical or unique take on a test - related story.