Percy is surely one of the main characters, as the story is centered around him being left for dead. There might also be the people who left him, though we don't know who they are yet. Maybe there will be a character who discovers Percy and helps him, like a kind - hearted stranger.
The main character is obviously Percy. In addition to him, there could be his friends or comrades from his previous adventures. Even if they are not directly involved in leaving him for dead, they could play a role in his survival or in his search for justice. And there may be an antagonist, the one behind the act of leaving Percy for dead, who could be a powerful enemy with a hidden motive.
Since I don't know the exact 'left for dead true story', I can't say for sure who the main characters are. But usually, there would be the victim who was left for dead and perhaps the people who left them in that situation.
The main characters are a group of survivors. Usually, they are presented as a diverse set of individuals with different skills and personalities. They could be a tough - looking guy who is good at combat, a more level - headed person who can strategize, a young and agile one, and perhaps someone with medical knowledge. But the exact details are often left open - ended to some extent in the 'left 4 dead graphic novel' to allow readers to imagine.
One possible plot could be Percy's struggle for survival in a harsh and unforgiving environment. Maybe he has to find food and water while fending off dangerous creatures. Another plot could involve Percy trying to figure out who left him for dead and seeking revenge.
It could be a rogue ninja from another village who has a vendetta against Naruto. This ninja might have set a very elaborate trap that made it seem like Naruto was killed and left his body in a place where his friends would find him and think he was dead.
I'm not sure exactly who the main characters are without seeing the film. But they could be the survivors of the situation who were left for dead.
The Titans might not be completely defeated. Some of their followers could be plotting against Percy. They think that by getting rid of him, they can start a new uprising against the gods. So, they leave him in a dangerous situation where they believe he will surely die.
Well, without actually reading the fanfic, it's hard to say for sure. But it could be his friends. In many fanfics, there are often sidekicks or best friends who play important roles. They might support Percy in his adventures or add some comic relief to the story.
There could be new characters introduced as well. Maybe other gods or demigods who have a particular interest in Percy's new - found godhood. They could either be allies or antagonists, depending on their motives and how Percy's new power impacts the existing power balance in the fanfic's universe.
Obviously, Naruto would be one of the main characters. Depending on the specific plot, Sasuke could also be involved. He might be one of the ones who either helps Naruto or is part of the reason Naruto is left to die. Sakura could also play a role, maybe she has a change of heart towards Naruto in the fanfic.
The main characters would be a mix of both universes. From Left 4 Dead, all four of the main survivors would play important roles. They would interact with characters from the Nazi Zombie side. It could be a group of resistance fighters led by a fearless commander. There might also be a character who is a hybrid of sorts, perhaps a survivor who was experimented on by the Nazi zombie creators and now has some unique abilities. This character could act as a bridge between the two groups, helping the Left 4 Dead survivors understand the nature of the Nazi zombies and how to defeat them.