How about a character who is a meta - human with the ability to sense when someone is hiding their true identity? This character could initially be a mystery to Batman, not sure if they are friend or foe. As the story progresses, they could become an important ally in protecting Batman's secret, while also challenging Batman's views on his own identity and the need for secrecy.
The Riddler's daughter could be an interesting addition. She could be a brilliant detective herself, but conflicted about her father's criminal ways and her own feelings towards Batman.
One idea could be exploring what if Bruce Wayne's identity as Batman was exposed accidentally by a new high - tech surveillance system in Gotham. Another could be a story where Batman has to take on a new identity temporarily to infiltrate a secret criminal organization that has been studying his every move as Batman.
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.
The Riddler could be added. He could be constantly trying to figure out what lies behind Batman's mask, both literally and metaphorically. His mind - games could force Batman to confront things about himself that he usually keeps hidden.
Batman's allies like Robin (whichever version - Dick Grayson, Jason Todd etc.) are often involved. They might have to deal with the fact that their mentor's identity is now public and face new threats because of it. Also, Commissioner Gordon is a main character. His relationship with Batman has always been complex, and this revelation will surely change how they interact.
One idea could be that Terry's identity is revealed to the public. This would lead to chaos as his enemies target his family and friends directly. His mother might be in danger, and he'd have to constantly protect her while still trying to fight crime. It could also make his relationship with Dana more complicated, as she now has to deal with the fact that her boyfriend is Batman.
One consequence could be that his enemies might target Gordon to get to him. Since Gordon now knows his identity, if the bad guys find out, they could use Gordon as a way to harm Batman.
One interesting plotline could be the reaction of Gotham's criminals. They might either be overconfident thinking they can now easily target Batman or be terrified knowing his true identity means he has more resources at his disposal. Another could be how Batman's allies, like Alfred, deal with the new situation. Alfred might be even more protective or start to worry about the safety of Bruce Wayne's loved ones.
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.
Obviously, Batman/Bruce Wayne himself is a central character. His life would be turned upside down by the revelation of his identity.
Batman's identity in Justice League fanfiction is often a source of mystery and intrigue. Writers may play with the idea of a new villain discovering who he really is. This could be through hacking into Wayne Enterprises' systems or following his trail from Gotham to the Justice League's operations. The fanfiction might also explore how Batman himself feels about protecting his identity within the team. He might be constantly on guard, fearing that if his identity as Bruce Wayne is revealed, it could put his loved ones in danger even more than they already are.