A theme that frequently appears is redemption. Sometimes Batman might be in a situation because of a mistake he made, and Superman saving him is a form of redemption. Also, the theme of heroism is prominent. Superman's act of saving Batman reaffirms their status as heroes and shows their selfless nature towards each other.
When Batman saves Superman, it could make him more confident in his own abilities outside of his normal Gotham - based operations. He realizes that his skills as a detective, strategist, and fighter are not just useful in his own city but can be applied on a much larger scale. This could lead to him being more involved in Justice League - related matters and having a more positive outlook on working with super - powered individuals in general. He might also become more empathetic as he gets to understand Superman's vulnerabilities better.
Well, one popular 'superman saves batman fanfiction' is 'The Rescue in Gotham'. In this story, Superman arrives just in time to save Batman from a powerful new villain who has him cornered in an abandoned warehouse. The action scenes are really well - written, and it shows a great dynamic between the two heroes.
Lex Luthor is often a main antagonist. He might be the one who sets up the situation where Superman needs to be saved, like creating a powerful weapon or a devious plan to weaken Superman.
One possible storyline could be that Batman has to use his detective skills to find out a hidden threat to Superman before saving him. Maybe there's a kryptonite - based weapon that only Batman can detect and disable.
One possible reason could be mind control. Maybe some villain has taken over Superman's mind and made him do it. Another reason might be a fundamental difference in their ideologies that has escalated to the point of no return.
Lois Lane is often a popular character. In fanfiction, she might play a crucial role in mediating between Batman and Superman or getting involved in their adventures in a more hands - on way, using her investigative journalism skills.
Alfred Pennyworth is quite popular too. He can offer his wisdom and support to Batman, and his interactions with Superman can be both humorous and heartwarming. He's like the glue that holds things together in the Batcave, and his presence can bring a sense of home to the story.
One possible scenario in Batman saves Batgirl fanfiction could be that Batgirl is in a dangerous situation, like being held captive by a powerful villain. Batman, with his detective skills and combat abilities, manages to find her location and battles the villain to rescue her. It's a classic superhero - damsel in distress (although Batgirl is also a superhero in her own right) situation that often plays out in fanfiction.
In Batman and Superman fanfiction, 'stranger danger' can be depicted in various ways. For example, a new villain could be introduced who is a stranger to the city and poses a great danger. The heroes would then have to figure out the stranger's motives and powers to stop them. It adds an element of mystery and suspense to the story.