I'm not sure as I haven't read it, but usually there are protagonists and antagonists.
I'm afraid I don't know the specific main characters in this light novel. However, if we assume based on the title, the main character would be the notorious talker. There could be other characters like a sidekick who is constantly listening to the talker's ramblings, or an antagonist who gets frustrated with the talker's constant chatter and tries to silence them in some way.
It's a story full of mystery and intrigue. It likely involves complex characters and a plot that keeps you guessing.
The main characters are the Navajo code talkers. These are young Navajo men who are recruited to serve in the military. There are also likely military officers who interact with them, some of whom may be initially skeptical of the Navajo code but later come to rely on it. And perhaps family members back on the Navajo reservation who are part of the code talkers' backstory and motivation.
The main characters are the seven members of the Secret 7 club.
There might be a female lead who is at the center of the secrets. For example, she could be a woman with a past she is trying to hide, and her actions and relationships are shaped by this need to keep things in secret.
The two main characters in 'Secret Window, Secret Garden' are Mort Rainey and John Shooter. Mort Rainey is a writer living his life when suddenly he is faced with this strange situation. John Shooter, who appears out of nowhere, is the catalyst for all the chaos in Mort's life. Mort is the character we follow through his psychological journey as he tries to figure out what's going on with Shooter's claims. Shooter is the mysterious and somewhat threatening figure that forces Mort to re - evaluate his own work and sanity.
In 'the secret billionaire novel', the main character is surely the secret billionaire. There may be a confidant, someone the billionaire trusts with their secret or at least part of it. There could also be antagonists, like those who are trying to expose the billionaire's secret for their own gain. Additionally, there might be ordinary people with whom the billionaire forms relationships, which are influenced by the hidden wealth.
I don't know the exact main characters as I haven't read the novel. But they could be scientists or adventurers.
Not having read 'the secret stealers a novel', it's tough to name the main characters. However, in a story about stealing secrets, we might expect to find a mastermind behind the secret - stealing operations. This could be a shadowy figure with a complex backstory and motives. Then there would likely be those who are affected by the stolen secrets, like victims or people whose lives are in danger because of the secrets being exposed. And of course, there could be characters who are on a quest to expose the secret stealers and bring them to justice.
I don't know as I haven't read the book. But it could be a family, like a mother, father and their children. Maybe there's also a friendly neighbor or a mysterious stranger who plays a crucial role.