One idea could be a story where Batman has a really bad birthday because all his gadgets malfunction on that day. Maybe his Batmobile breaks down right in the middle of chasing a villain, and his grappling hook doesn't work when he tries to escape a dangerous situation.
A different bad Batman birthday fanfiction could involve Batman forgetting his own birthday because he's so caught up in fighting crime. His friends, like Alfred, try to plan a celebration but it all goes wrong. Alfred accidentally burns the birthday cake while trying to keep the Bat - computer from getting hacked by a new villain who has targeted Batman specifically on his birthday.
Another idea is that on Batman's birthday, all the villains in Gotham City team up to throw him a 'bad' birthday party. They set up a series of traps instead of normal party things. They could fill the Batcave with their own versions of party decorations like Joker - themed balloons that are actually bombs waiting to explode.
One idea could be that on Batman's birthday, all the villains in Gotham decide to team up and give him a 'gift' of a city - wide crime spree. Another could be a flashback to Bruce Wayne's childhood birthdays and how they influenced his journey to becoming Batman. Or perhaps on his birthday, Batman discovers a long - lost family heirloom that has a secret connection to his crime - fighting mission.
Another idea might be that one Batman is from the future and has come back to meet his past self. The future Batman could show the past version some new technologies and tactics, but also warn him about the potential consequences of certain actions. This could lead to self - reflection for the past Batman and a change in his approach to crime - fighting.
To write a really engaging bad Batman birthday fanfiction, create a sense of chaos. Let the events spiral out of control. Batman is used to being in control, but on his birthday, everything is topsy - turvy. His allies might be preoccupied with other things. Robin could be on a school trip and not able to be there. The city might be in more chaos than usual, with fires breaking out everywhere. And Batman is left to deal with it all while also trying to figure out why his birthday has become such a disaster.
One idea could be a story where Robin has to take on Batman's role temporarily when Batman is injured. He has to face a powerful villain all on his own, using the skills Batman taught him in a new and creative way.
One idea could be a crossover where Naruto is transported to Gotham City. He might use his ninja skills to help Batman fight the villains in a new and unexpected way. For example, his ability to move quickly and stealthily could be a great asset in tracking down the Joker.
One idea could be a story where Batman and Hawkgirl team up to stop a powerful villain that is causing chaos in both Gotham and Hawkgirl's home realm. They start off not trusting each other fully due to their different methods, but as they face challenges together, they learn to respect and rely on one another.
Another idea could be the contrast between Batman's brooding and often solitary nature and the more community - based and female - dominated society of Themyscira. This could lead to some character development for Batman as he learns new ways of interacting and trusting others.
One idea could be a crossover where Batman and the Turtles team up to take on a common enemy like the Foot Clan and some of Batman's rogues gallery working together. Maybe they meet in Gotham City and have to adapt to each other's fighting styles.
One idea could be a story where Batman and Wolverine team up to take on a powerful new villain in Gotham City. The contrast between Batman's high - tech gadgets and Wolverine's brute strength would make for an exciting dynamic.
In some Punisher Batman fanfiction, the setting might be a Gotham overrun by more extreme and violent criminals. The Punisher could come to Gotham thinking he can clean it up better than Batman. This would lead to a power struggle and also a chance for them to learn from each other's techniques.