Obviously, Batman/Bruce Wayne himself. His butler Alfred would also be heavily involved as he has always been there to support Bruce. Alfred would likely be trying to protect Bruce and keep his remaining secrets safe.
Batman's fellow Justice League members could be involved. Superman might try to help Batman deal with the situation. He could offer his support both publicly and privately, maybe even helping to protect Bruce Wayne's family and assets while Batman tries to regain some control over the situation.
Obviously, Batman/Bruce Wayne himself is a central character. His life would be turned upside down by the revelation of his identity.
Henry is the main one for sure. Ray, his mentor, would also be a big part of it. Ray might have to deal with the fallout of Henry's identity being out in the open, like handling the media and the public's reaction. Also, Henry's family could be involved. His parents might be worried about his safety now that his identity is known. And then there are the other minor characters from the show who could either support Henry or turn against him depending on the plot.
Obviously, Batman/Bruce Wayne himself is at the center. Alfred Pennyworth would be very involved as he has known Batman's identity all along and would likely be trying to protect it or deal with the consequences if it's revealed. Commissioner Gordon might also play a big role. He has a close relationship with Batman and would be affected by the revelation. Then there are the villains. The Joker could be one of the main villains in such a story, using the revelation to his advantage in some devious way.
One possible plotline could be the chaos that ensues in Gotham when Batman's secret identity is revealed. His enemies might target his loved ones directly. For example, the Joker could go after Bruce Wayne's family and friends in a more brazen way than before.
Batman's allies such as Commissioner Gordon could be involved. Sometimes Batman might be angry at Gordon if he feels that the police force is not doing enough to support his fight against crime. Also, other members of the Bat - family like Batgirl could be part of the story. Their actions or decisions might trigger Batman's anger. For instance, if Batgirl decides to take on a powerful villain alone against Batman's advice.
Batman himself is obviously one of the main characters. Since it's about his identity being revealed, he would be at the center of the story dealing with all the consequences.
Obviously, all of the Avengers would be affected. But characters like Iron Man/Tony Stark would be a big focus. His playboy billionaire image could be completely changed in the public eye once his superhero identity is out. Also, Spider - Man if he's part of the Avengers in the fanfiction. His young age and normal life with Aunt May would be greatly disrupted.
In addition to Danny and his immediate circle, there could be other characters from the Danny Phantom universe. For example, Valerie Gray. If she discovers Danny's identity, she might have a complex reaction. On one hand, she's been hunting ghosts, but on the other, Danny has also been protecting the town. So, her role in the fanfiction could be very interesting, especially in terms of how she interacts with Danny after the identity reveal.
Obviously, Ladybug and Chat Noir are often central. Marinette, who is Ladybug, and Adrien, who is Chat Noir. Also, Hawk Moth as the main villain often plays a role in these fanfictions when the identity is about to be revealed or has been revealed, as his actions can be related to this big event.
In the 'naruto heritage revealed fanfic', Naruto will surely be a central figure as the story seems to revolve around his heritage. Besides him, characters like Kakashi might be involved as he has knowledge about Naruto's father. Also, characters from the Uzumaki clan could play important roles as Naruto is from that clan. And of course, Jiraiya, Naruto's mentor, who knew a lot about Naruto's family history and the ninja world in general, might be included to help uncover more about Naruto's heritage.