It could be that she is a secret heir to an ancient magical family. In many fanfics, this trope is used to add an extra layer of mystery and power to her character.
When she has a secret identity as a powerful dark wizard's daughter (even if she doesn't follow the dark ways), it creates a lot of tension. Her friends might suspect her at times, and she has to constantly prove her loyalty. This adds a whole new level of drama to the fanfic, like in a story where Harry and Ron start to question her actions because of rumors about her heritage.
She could have a secret identity as a time - traveling agent. In this fanfiction, Hermione discovers a way to time - travel without the use of a Time - Turner. She uses this ability to secretly correct historical mistakes in the wizarding world, all while keeping her identity hidden from her friends.
First, decide on her secret identity. Let's say she's a spy for an underground resistance against the Dark Arts. Then, start with a situation where her normal life at Hogwarts is disrupted. For instance, she starts receiving mysterious messages that seem to be related to her secret work. This can lead to her having to sneak around Hogwarts, using her magic in ways that her friends don't suspect to communicate with her contacts in the resistance.
Secret identities in novels enhance the plot by providing a source of intrigue. In 'The Scarlet Pimpernel', the mystery around Sir Percy Blakeney's true identity as the Scarlet Pimpernel keeps the readers guessing. It also enables the character to move in different social circles with ease. Since the Scarlet Pimpernel is known as a hero by some and Sir Percy is a well - known aristocrat, he can gather information and carry out his rescues more effectively. In a similar way, in novels like 'Shadowhunter Chronicles', characters often have secret identities which are crucial for their survival in the dangerous world of demons and magic. These secret identities allow for unexpected plot twists. For example, when a character's secret identity is finally revealed, it can change the entire dynamic of the relationships and power structures within the story.
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.
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.
Well, the secret identity might be someone who leads a double life, like a spy or a person with a forbidden power. It often drives the plot and keeps readers guessing.
One common theme is secrecy and the struggle to keep the child's identity hidden. There's also often the theme of the child being an outcast due to their unusual parentage. Another theme could be the discovery of the child's true heritage and how it impacts their understanding of themselves and the world around them.