The Joker could be an antagonist even when Batman becomes a god. He might see Batman's new status as a challenge and try to bring him down to his level through his usual chaotic and insane methods. Maybe he'd try to drive Batman mad with the idea that his new powers make him no better than the villains he fights.
Perhaps in the 'batman becomes a god fanfic', a plotline could involve Batman facing off against other god - like entities. He has to prove himself worthy of his new status among these powerful beings. This could lead to epic battles and alliances as he tries to protect not just Gotham, but the entire world or even the universe from threats that only a god - Batman could handle.
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.
One possible plotline could be Batman using his new god - like powers to completely reform Gotham in an instant. He could eliminate all crime, poverty, and corruption with a single thought. Another might be him facing off against other god - like beings from different mythologies who see him as a threat to the balance of power in the universe.
In a 'Naruto becomes the Batman' fanfic, Naruto might start adopting Batman's methods. He could become more stealthy and rely on his intelligence more. For example, he might use gadgets similar to Batman's utility belt, like smoke bombs or grappling hooks. Also, his approach to justice could change. Instead of his usual straightforward ninja battles, he might start planning more strategically, much like how Batman plans his crime - fighting operations in the dark alleys of Gotham.
In a fanfic where Batman becomes a lantern, his character would likely undergo some changes. The lantern power might give him new insights into the emotional spectrum. For example, if he were a Green Lantern, his willpower could be enhanced even more. He could also face new challenges as he has to deal with the Lantern Corps' politics and enemies. It would be a great opportunity to explore how Batman's dark and brooding nature would interact with the more cosmic and colorful Lantern world.
Well, perhaps Percy discovers some ancient power within himself that gradually transforms him into a god. He might have to face a series of trials to fully ascend, like battling powerful monsters or making difficult moral choices.
Naruto's personality would become more brooding. He would be less impulsive and more calculating, like Batman. He might not be as openly friendly as he was before, keeping his thoughts and plans more to himself.
There were a few novels that could be recommended to readers who liked the female protagonist turning into Batman. Among them,"The Strongest Female Lead in the Heavens" was a light novel written by the author, Drunken Smile. It told the story of the female protagonist who turned into Batman after responding to begging. In addition,"Days of Being a Batman in American Comics" was a light novel/derivative doujinshi novel written by the people in the house. The characters included Bruce Wayne, the Batman. However, due to the limitations of the search results, no more detailed information or other recommendations could be provided.
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.