The story could begin with Buffy not knowing about her true father. She's living her normal slayer life when suddenly she discovers that she's related to Bruce Wayne. This revelation could open up a whole new world of possibilities for her. She could gain access to WayneTech and use it to develop new tools for slaying. And she might have to deal with the Bat - family, some of whom might be skeptical of her at first, but over time, they come to accept and even rely on her unique skills.
In this fanfic, Buffy might struggle with the expectations of being Bruce Wayne's daughter. She's used to her own world of slaying vampires and demons, but now she has to deal with the high - society life in Gotham. She could rebel against Bruce's over - protectiveness while still trying to uphold the family name in the public eye. Also, she might introduce some of her friends from Sunnydale to the Gotham scene, causing quite a stir.
At first, it could be a bit rocky. Bruce is used to his own way of doing things and Buffy has her own independent streak. But they would gradually learn to respect each other. Bruce might be impressed by Buffy's combat skills and her ability to handle the supernatural. Buffy, on the other hand, could learn a lot from Bruce's strategic thinking.
He might develop a greater sense of humility. Without the Batman persona to fall back on, he has to face his own limitations as a person. For example, he may struggle to get people to listen to his ideas for change when he doesn't have the intimidation factor of Batman.
To incorporate the different aspects of Bruce Wayne's life in a birthday fanfic, you could have the story begin with Bruce waking up on his birthday. As he goes about his morning routine, we see his normal, human side. Then, as he starts getting ready for his birthday event, we can see the influence of his wealth and status. During the event, he could have a conversation with an old friend from his school days, which shows his past. And when a threat emerges in Gotham during the party, his Batman side takes over. His loyalty to Gotham and his determination to protect it are on full display as he leaves the party to deal with the situation.
One common theme could be the daughter's struggle with living in the shadow of her father's legacy. She might be trying to prove herself as a hero in her own right. Another theme could be family relationships. For example, how she interacts with Bruce Wayne as a father, dealing with his overprotectiveness or his high expectations. Also, the theme of identity might be present. Is she a vigilante like her father? Or does she choose a different path to make an impact in Gotham?
One great fanfic is 'The Father - Son Bond'. It beautifully explores the complex relationship between Bruce and Damian. It shows how Bruce tries to be a good father while also dealing with his role as Batman, and Damian's struggle to fit into this new world with his own strong - willed nature.
Well, in such a fanfic, it might show Bruce Wayne as a completely different entity from Batman. Maybe Bruce is just a normal rich guy who has no idea about the vigilante activities of Batman. He could be living his own life, focused on business and social events, while Batman is someone else entirely, perhaps an unknown figure with no connection to the Wayne family.
Maybe in the fanfic, there's a threat to the Wayne family fortune. Terry and Bruce have to work together, with the rest of the family, to protect it. This could involve using their wits and skills in different ways, and also show how the family members support each other in tough times.
Another aspect could be that in some darker fanfics, if Bruce Wayne were to cross a moral line, perhaps Alfred would have to take more extreme measures. He might cut off Bruce's financial resources related to his vigilante activities. This would force Bruce to re - evaluate his actions and the way he operates as Batman. It's a way of punishing him to make him understand the importance of ethics even in his fight against crime.
In a fanfic, Bruce Wayne could be an exchange student from a foreign country where there are no Quirks but advanced technology. He could introduce new concepts of heroism that are more about using gadgets and strategic thinking rather than relying solely on Quirks. He would also be a bit of an enigma to the characters in My Hero Academia, as his methods are so different from what they're used to.
To write a good character for the daughter, give her her own personality traits. She could be kind - hearted but also have a bit of a feisty side. For example, she might be always helping out at local charities but also not be afraid to speak her mind when she disagrees with something Bruce does.