There probably is. Given the popularity of both Darkseid and Batman in the DC universe, it's a common and rather dark theme for fanfiction writers to explore. Some might write it to show the extreme power of Darkseid, while others may use it as a starting point for a more complex alternate universe story where Batman's death has far - reaching consequences for other characters.
One possible plotline could be that Darkseid is about to destroy Gotham or Earth in a way that Batman has no other option but to kill him. Maybe all of Batman's usual gadgets and allies are useless, and he has to use a kryptonite - like weapon (if it could affect Darkseid) to take him down.
A 'Darkseid Kills Batman' fanfiction could center around the build - up to Batman's death. It might show Batman's attempts to outwit Darkseid but ultimately failing. Then, it could explore the aftermath, such as how Gotham descends into chaos without its protector, and how the Justice League is affected. There could also be a sub - plot about a character seeking revenge for Batman's death.
It's a somewhat unique concept. In the mainstream DC universe, Darkseid is an extremely powerful villain. For Batman to kill him in fanfiction goes against the norm where Batman usually uses his wits and non - lethal means. It shows the creativity of fanfic writers who want to explore extreme scenarios and different power dynamics.
Batman would be in a tough spot. Darkseid is extremely powerful. But Batman is not one to give up easily. He might try to analyze Darkseid's powers and find a way to counter them, even in captivity.
Well, if Darkseid kidnaps Batman in a fanfiction, it could lead to an interesting exploration of Batman's character. He'd be out of his element, in Darkseid's domain. But Batman has a strong will. He might try to understand Darkseid's motives while looking for an opportunity to turn the tables. It could also show how the other characters in the Batman universe react to his disappearance.
If Batman were to join Darkseid, it would be a huge shift in the DC universe. Batman is known for his strong moral code and fighting against evil. Joining Darkseid would mean he has to abandon his principles. Maybe he's forced to do it under some mind - control or a desperate situation to save Gotham in a way he thinks only Darkseid can help. But it would also make him a target for all his former allies, like the Justice League.
If Batman was raised by Darkseid, he would likely be a very different character. His moral code might be warped. He could be more brutal and less hesitant to use extreme measures. Instead of fighting for justice in Gotham, he might be used to enforce Darkseid's rule across the universe.
In such a fanfiction, the story might develop as Batman discovers secrets about Darkseid that he thinks he can use to his advantage. He could be playing a long - game, pretending to be on Darkseid's side while actually planning to bring him down. However, Darkseid is no fool and would likely test Batman's loyalty. Meanwhile, the rest of the DC universe would be in chaos as they try to figure out why Batman has turned and how to stop him if he's truly gone bad.
I don't think it's a common concept. Most Batman fans love the character for his moral code which includes not killing. Fanfiction usually tries to expand on the existing lore in a way that is somewhat in line with the general perception of the character. So, stories where Batman kills are more of an exception rather than the norm in the fan community.