Obviously, Naruto is the central character as the title 'naruto goes mad' implies. Sasuke often plays a crucial role too. He might be the cause of Naruto's madness in some cases, like if he betrays Naruto again in a more extreme way. Sakura could also be involved, perhaps trying to bring Naruto back from his madness. And Kakashi, as Naruto's former teacher, may try to figure out what's wrong with Naruto and find a way to help him.
The main character is Naruto without a doubt. However, characters from the Hidden Leaf village council may also be involved. Their decisions, such as how they treat Naruto or the secrets they keep from him, could lead to his madness. Additionally, characters like Hinata might be in the story. Hinata could be one of the few who still believes in Naruto even when he goes mad and tries to reach out to him and calm him down.
Naruto is the main focus, of course. But other characters like Jiraiya could be involved. In some fanfictions, Jiraiya might have left behind some knowledge or a prophecy that, when misinterpreted or when things don't go as expected, could contribute to Naruto's madness. Also, characters from the Akatsuki could be part of the story. They might take advantage of Naruto's vulnerable mental state to try and manipulate him for their own purposes.
Well, obviously Harry Potter himself is the central character. Hermione and Ron are almost always involved too. They would be the ones trying to figure out what's wrong with Harry and how to fix him. Dumbledore might also play a major role, as he often has deep knowledge about magic and could potentially help Harry regain his sanity.
Well, Naruto is almost always one of the main characters. Since it's Naruto - themed fanfiction. And of course, the mad chemist is another main character. They could be a new character created specifically for the fanfiction, or it could be an existing character from the Naruto universe who has taken on the role of a mad chemist, like Orochimaru perhaps.
Often, the main characters are Naruto and his friends. Naruto, as the protagonist, is naturally drawn to the mystery of the egg. His friends like Shikamaru, who is intelligent and can strategize about how to deal with the situation regarding the egg, and Choji, who might provide some physical protection if needed. Hinata could also be involved, perhaps having a special connection to the egg because of her Byakugan. And then there are the villains, like the members of the Sound Five, who might want to get their hands on the egg for their own evil purposes.
Naruto himself is almost always involved as he is the main character of the Naruto series. His friends like Sasuke and Sakura may also be part of the story. Sometimes, even villains like Orochimaru or Madara could be involved if the plot of the fanfiction is related to a big threat where their knowledge or power is needed.
Obviously, Naruto himself is the central character as it's about him 'snapping'. Sasuke is also often involved. He might be a factor in what causes Naruto to snap, or he could be on the receiving end if Naruto's snapping is directed at his actions or decisions.
In 'naruto angry fanfiction', characters like Hinata can also be involved. If she is in danger or if Naruto feels that he couldn't protect her well enough, it can stir his anger. And villains like Orochimaru or Madara can be present as they are often the source of problems that make Naruto angry, whether it's through attacking the village or harming his friends.
The main characters are Sam and Dean Winchester, of course. But in some fanfictions, Bobby Singer might also be involved. Since he was like a father figure to them, he could be the one guiding them through the time - travel process, or he could be there in the past waiting for them. Also, the characters of their parents, Mary and John Winchester, might show up if they go back to a time when their parents were alive.
Neville Longbottom can also be a main character in some 'Harry Potter goes back in time' fanfictions. Given his growth and importance in the original series, in the fanfic, Harry might go back and help Neville become more confident earlier. This could have a significant impact on the fight against Voldemort as Neville could then be an even more powerful ally from an earlier time.
Obviously Naruto is the main character as he is the one usually pulling the pranks. His friends like Shikamaru might also be involved, either as victims of the pranks or as accomplices. Sakura could be in there too, perhaps getting annoyed at Naruto's pranks or being part of a prank on someone else.
Obviously Naruto is the main character. And sometimes his parents might be involved in a more complex way, like through flashbacks or alternate storylines where they had reasons for the so - called 'abandonment'.