Since we don't know the details of the '7th man story', the main characters could be the 7th man himself and the people around him in the story.
The most obvious main character is the 7th man. But in a story, there are often other characters who interact with the main one. In this case, there could be comrades if he was in a group situation, or perhaps an antagonist who causes problems for him. There might also be a love interest, which could add an emotional layer to the story. Without reading the story in detail, it's hard to name all the main characters precisely, but the 7th man is surely at the center of it.
The main character is the 7th man himself. He is the narrator and the one whose experiences the story focuses on. His friend, who was taken by the wave, is also an important character, though we don't get as much direct information about him.
I don't know the exact main characters as I haven't read the novel. But surely, the 8th man is one of the main characters. There might be his friends or foes who play important roles in the story.
The main character is surely the 12th man. He is the focal point of the story. Besides him, there might be characters like his comrades in a military - like scenario, or his teammates in a sports - related story. Maybe there are also antagonists or challenges in the form of opposing forces or difficult situations that he has to face, which could be personified as characters in a way. For example, in a military story, the enemy soldiers or the harsh weather conditions could be considered as 'characters' that interact with the 12th man.
As I haven't read the '12th man malayalam story', I can't say for sure what the main characters are.
I'm not able to recall the main characters in the Decameron's 5th day 4th story precisely. However, in the Decameron, characters often include young lovers, wise elders, and cunning servants. It's possible that the 5th day 4th story also features such types of characters, who get involved in complex relationships and situations that drive the plot forward.
Since I haven't studied the 'decameron 5th day 9th story', we can only make some speculations. It may have a male protagonist who is on a quest for something, perhaps love or wealth. There might be a female character who is either an object of his affection or an obstacle in his path. And there could also be other supporting characters like friends or family members who influence the actions and decisions of the main characters.
In the 'the 8th man creepypasta story', it's most likely the 8th man. He is the one that gives the story its unique and spooky flavor. He might be presented as an enigma, with his actions and presence being the driving force of the story. Other characters may be there just to react to him and to show how strange and terrifying he is.
It might be an athlete. In the context of sports and the idea of the 12th man being the fans, the main character could be a key player on a Norwegian sports team who was greatly influenced by the support of the 12th man (the fans). The player's performance and the story of how the fans' support impacted him could be central to the story.
Since we don't know the full story, the main character is likely the 19th wife herself. There may also be her husband as an important character.