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.
Obviously, Leo Valdez is the central character. But often, his friends from the series like Percy Jackson, Annabeth Chase, and Piper McLean are also involved. They play important roles in either causing the situation that makes Leo snap or in helping him deal with the aftermath of his snapping.
Obviously, Ruby herself is the central character. But often, her team members like Weiss, Blake, and Yang are also involved. They play important roles in either causing the situation where Ruby snaps or in helping her get through it.
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.
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.
Well, Mikasa herself is obviously a main character in these fanfictions. Since it's about her snapping, she is at the center of the story most of the time. Eren is also often involved. Given their complex relationship in the original series, his actions or words could be the trigger for Mikasa to snap. Another character that might be involved is Armin. He could be the one who tries to calm Mikasa down or understand what made her snap.
Well, obviously Darth Vader is the central character. But often, other characters like Luke Skywalker can be involved. Maybe Luke tries to reach out to Vader during his 'snap' moment, hoping to turn him back to the light side.
Obviously Naruto himself is the central character as it's about his lifeless eyes. Sakura could also be involved as she is one of Naruto's closest friends. She might be the one to notice the change in his eyes first and try to help him.
Obviously, Naruto himself is the central character. But other characters like Sakura might also be involved. She could be the one trying to get Naruto sober or scolding him for his drunken behavior.
Obviously Naruto himself is the central character as the story is about him cutting himself. Sakura is often involved as well. She is Naruto's friend and a medical ninja. So she might be the one to discover Naruto's self - harm and try to heal him both physically and mentally.