Obviously, Batman himself would be one of the main characters. And his son, who could be Damian Wayne, for example. There might also be Alfred, as he is often involved in the Bat - family's affairs and could be present during or contribute to the talk in some way.
It could be about Batman imparting some important life lessons or crime - fighting wisdom to his son. Maybe he's teaching him about the importance of justice and how to handle the responsibilities that come with being a vigilante.
Well, in fanfiction, 'batman gives the talk' could cover a wide range of things. It might be Batman giving a motivational talk to the police force in Gotham to boost their morale in the fight against crime. Or perhaps he's giving a talk to a young protege, sharing his wisdom about the responsibilities that come with power. It could also be him addressing the public about some new initiative he has to make Gotham safer.
Another possibility is that the audience is the criminals of Gotham. Batman might be trying to give them a chance to reform by giving a talk about the consequences of their actions and the possibility of redemption. He could be using his presence and words to intimidate them into changing their ways or at least thinking twice before committing more crimes.
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.
Well, in batman vs justice league fanfiction, characters like Nightwing and Oracle are prime candidates to side with Batman. Nightwing was Batman's first Robin and has a loyalty to him. Oracle, with her intelligence and access to information, would back Batman if she believed his cause was just. Additionally, characters like Batgirl could also side with Batman, especially if she thought the Justice League was overstepping its bounds.
Wonder Woman could also be involved. She might be caught in the middle, trying to stop the fight at first. But if she realizes that Superman is being a threat for some reason, she could side with Batman, or at least not interfere in Batman's attempt to defeat Superman.
Oracle, or Barbara Gordon. She has a deep connection to Batman, having worked with him in the past. Her intelligence and tech - savvy skills could add an interesting dynamic to the harem. She can be both a source of support and an independent force within the group.
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.
Obviously, Nightwing himself would be the main character as he's the one taking on the Batman role. Robin, if there's a younger Robin at the time in the fanfiction, would also be a key character. He might look up to Nightwing in his new role or have some doubts about him filling Batman's shoes.
Obviously, Batman himself. He is the central figure of the family. Then there's Alfred, who is like the family's butler and caretaker. He would be the one preparing the dinner. Robin, whether it's Dick Grayson, Jason Todd, or any of the other Robins, would often be present. Batgirl could also be there, adding a female presence to the group.