In a fanfiction where Batman becomes immortal, one possibility is that he would become extremely jaded over time. He has seen so much death and destruction in Gotham, and with immortality, that would only continue indefinitely. He might start to question his own motives and methods. Also, his relationships with other characters like Alfred, Robin, and Commissioner Gordon would be strained. They would age and die while he remained, which could lead to him isolating himself from the mortal world.
His character would likely become more complex. He might struggle with the idea of outliving everyone he cares about. His sense of purpose could shift from just protecting Gotham to something larger, like finding a way to end all crime globally since he now has all the time in the world.
One possibility could be that Batman, after facing one too many betrayals in Gotham, decides to take a different path. Maybe the constant struggle against crime with little real change in the city makes him cynical. He could start using his skills and resources to control the underworld instead of fighting it. For example, he might start dictating which criminals can operate and where, creating a new order that is still dark but under his command.
If Batman becomes Joker in fanfiction, Gotham would be in chaos. Batman is the symbol of justice and order, while Joker represents chaos and anarchy. Without Batman to protect the city, criminals would run wild. And as the new 'Joker', Batman might use his intelligence and skills in a very different and dangerous way, perhaps creating more harm than good.
If Batman becomes a Lantern in fanfiction, he would gain the power of the Lantern ring. This could enhance his combat abilities even further. He might use the ring's energy constructs in his crime - fighting, creating things like shields or grappling hooks. His detective skills combined with the Lantern powers would make him an even more formidable force in Gotham.
The Joker could still be a major villain. Even with Batman as a god, the Joker might find some twisted way to challenge him. Maybe he'd try to drive Batman to use his god - like powers in a way that goes against his moral code. Ra's al Ghul could also be a villain. He might see Batman's new godhood as a perversion of the natural order and seek to destroy him.
There's a fanfiction that focuses on Bruce's training with different martial arts masters around the world as part of his transformation into Batman. It shows his struggles, both physical and mental, as he tries to master the skills needed to fight crime in Gotham. The story also delves into how he acquires his high - tech gadgets during this time.
In this fanfiction, Izuku could be inspired by Batman's lack of superpowers but still being a formidable hero. He may start training in more martial arts and stealth techniques, similar to Batman. And he could even create his own set of gadgets, like grappling hooks and smoke bombs, to aid him in combat and rescue missions.
He might be motivated by a sense of futility. After years of fighting crime and seeing no real end to it, he could think that the only way to bring about change is to control the criminal underworld himself. So, he becomes a villain to enforce his own version of order.
Well, one way could be Sonic discovers Batman's comics in his world. Maybe Tails finds some strange artifacts that turn out to be from another dimension where Batman exists. Sonic reads the comics and is intrigued by Batman's determination and his no - kill rule. He starts to idolize Batman and tries to incorporate some of Batman's detective skills into his own adventures.