Kakashi is another character that is frequently involved. As Naruto's teacher, he would feel responsible for Naruto's situation. He might try to guide Naruto in controlling the Kyuubi's power, or he could be in a position of having to defend the village from a rampaging Naruto. Sakura too could be involved. She might be worried about Naruto and try to use her medical skills to help if Naruto gets injured during the process of dealing with the released Kyuubi.
Obviously, Naruto is the central character as it's about the Kyuubi being released from him. Sasuke also often plays a crucial role. He might be concerned about Naruto's new state, or he could be one of the characters trying to either help or stop Naruto depending on the plot.
Obviously, Naruto is the main character as he is the one releasing the Kyuubi. Sasuke could also be involved, perhaps as an ally or an antagonist depending on the plot of the fanfiction. Sakura might be there too, trying to support Naruto in controlling the Kyuubi's power or dealing with the aftermath.
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.
Naruto is usually a main character as he has a connection with the Kyuubi. Since he already has the Kyuubi sealed within him, it's logical that he would be the one to potentially unlock or develop the Kyuubi doujutsu. Sasuke might also be involved. His rivalry with Naruto could lead to interesting interactions in relation to the doujutsu, either trying to obtain it for himself or learning to counter it.
Kakashi could be involved as well. As Naruto's mentor, he would likely be concerned about Naruto's well - being and how he is handling the fusion. He might try to guide Naruto in controlling the power and also protect him from those who would seek to take advantage of his new - found strength.
Obviously Naruto and the Kyuubi are the main focuses. Since it's about their crossover, the story often revolves around their connection and how they interact with the new elements introduced in the crossover.
Naruto is the key protagonist without a doubt. The Kyuubi, being an integral part of Naruto's power and character, is also prominent. As for the harem, it often consists of various female characters from the Naruto series. For instance, Ino could be one of them. These characters are usually there to form the romantic relationships with Naruto, adding different flavors to the story depending on their personalities and their individual relationships with Naruto.
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.