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.
I'm not sure it's super popular. While the idea of Catwoman and Batman having a complex relationship is well - loved, the specific idea of Catwoman whipping Batman might be a bit more niche. However, in a community as large as the Batman fan community, there are bound to be some who enjoy exploring this more edgy and unusual concept.
It's an odd concept. Naruto is typically seen as a hero who values life and friendship. For him to kill Batman goes against his character. However, in the realm of fanfiction, anything can happen. Maybe the writer has a unique plot in mind, like a situation where Naruto is mind - controlled or there's some sort of misunderstanding between the two universes that leads to this extreme situation. But overall, it's not something you'd expect to see often.
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.
One common theme is chaos. With Batman gone, Gotham descends into utter chaos as the Joker runs amok. Another theme is revenge. Sometimes the story is about someone seeking revenge for Batman's death. Also, the exploration of the Joker's victory is a theme, showing how he relishes in finally killing his nemesis.
Often, there's a theme of justice being redefined. When Batman kills the Joker, it questions the traditional forms of justice in Gotham. It might also explore the theme of power. Does Batman become more of a tyrant or does he find a new way to use his power for good? And there could be a theme of redemption for Batman, as he tries to justify his actions to himself and others.
A common theme is the corruption of the hero. Batman is known for his strict moral code, so when he kills Robin, it shows a breakdown of that code. Another theme could be the exploration of the consequences of power. Batman has a great deal of power and influence, and killing Robin could be a way to show what happens when that power is misused.
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.
Yes, it is quite popular. Many fans are intrigued by the idea of Supergirl and Batman in a romantic relationship. They enjoy exploring the dynamic between the two powerful characters from different backgrounds. The contrast between Supergirl's more idealistic and hopeful nature and Batman's darker, brooding persona makes for an interesting romantic concept in fanfiction.
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.
One common theme is the corruption of power. Maybe Superman's power has gone to his head, and Batman sees the need to stop him at all costs. Another could be a mind - control scenario where Superman is being controlled by an outside force and Batman has no other option.