A great Arrow and Batman fanfiction could involve the two of them training together. Batman sharing his detective skills with Oliver and Oliver teaching Batman some of his more acrobatic and archery skills. This could lead to a stronger bond between them and help them both in their respective cities' crime - fighting efforts.
One idea could be Batman coming to Star City to help Arrow deal with a new, extremely dangerous criminal organization that has ties to Gotham. This could lead to some great fight scenes as they combine their skills and resources.
One popular 'Batman Arrow' fanfiction could be those that focus on a team - up between Batman and Green Arrow. They might face a common enemy like Ra's al Ghul who has plans that threaten both Gotham and Star City. In these stories, the different fighting styles and moral compasses of the two heroes are often explored.
One idea could be that Batman and Arrow team up to take on a common enemy like Ra's al Ghul. Since both of them have had run - ins with him in their respective storylines, it would be cool to see them combine their skills and resources to fight against him. Another plot could involve a mystery that spans both Gotham and Star City. Maybe there's a new criminal organization that's using technology from both cities to carry out their evil plans, and Batman and Arrow have to figure out how to stop them while also dealing with the differences in their methods of crime - fighting.
One idea could be that Arrow is transported to Gotham and teams up with Batman to take on a common enemy like Ra's al Ghul. They could combine their skills, with Arrow's archery and Batman's detective and combat skills.
A great plot could involve the two heroes swapping cities for a while. Arrow tries to deal with Gotham's crime underworld while Batman goes to Starling City to investigate a series of strange disappearances that might be linked to a powerful criminal organization there. This would lead to both heroes having to adapt to different environments and crime - fighting styles.
Well, perhaps Arrow is poisoned by a rare toxin that only Batman has the resources to find an antidote for. Batman races against time, using his network in the criminal underworld to track down the ingredients for the antidote. Meanwhile, he also has to fend off the villain's minions who are trying to stop him from saving Arrow. In the end, he manages to save Arrow just in the nick of time.
One interesting Arrow fanfiction could be about Oliver Queen having to face an enemy from a parallel universe. This would bring in new and exciting elements to the story as he has to adapt to different fighting styles and powers.
A really cool storyline might be a situation where they are both framed for a crime they didn't commit. They have to work together to clear their names while also dealing with their own personal issues. Batman might be suspicious of Green Arrow at first, and vice versa. This would create a lot of tension and drama. Also, a fanfiction where they are transported to an alternate universe and have to find their way back could be exciting. They would face new challenges and enemies that test their abilities in different ways.
I really like 'Green Arrow in Gotham'. In this fanfiction, Green Arrow finds himself in Gotham City and has to navigate the dark and dangerous world while also dealing with Batman's somewhat cold welcome. It's full of action and great character interactions.
There might be a story where the Black Arrow teams up with an unlikely ally. For example, a young thief who has a heart of gold. Together, they take on a powerful and corrupt lord in the region.