Another storyline might involve Batman leaving because of a personal crisis. For example, he discovers something dark about his past that makes him question his place in the Justice League. He might think that he's a liability to the team and decide to leave to protect them.
In some fanfictions, Batman could leave the Justice League because he wants to focus on protecting Gotham more exclusively. Gotham has always been his top priority, and he might feel that his time with the League is taking away from his ability to keep Gotham safe. He could decide that he can do more good on his own, in his own city.
One possible storyline could be that Batman discovers a conspiracy within the Justice League that endangers Gotham. So he and Robin decide to take on the League to stop it. Another could be that the Justice League is being mind - controlled, and Batman and Robin are the only ones who realize it and try to free their friends by fighting them. Or perhaps there's a misunderstanding where the Justice League believes Batman and Robin have turned bad, and they have to fight to prove their innocence.
One possible storyline could be that Batman sacrifices himself to save the world from a powerful alien threat. He uses his intellect to devise a plan that requires him to give his life. Another could be that he is poisoned by a new villain in the Justice League Unlimited universe, and despite the efforts of his friends, he succumbs to the poison.
One popular storyline could be an alternate universe where Batman has to lead the Justice League against a powerful, mind - controlling villain that has turned most of the world's population against them. In this, Batman uses his detective skills to find the source of the mind control while also trying to keep the remaining members of the Justice League from being captured.
Perhaps there's a story where Batman joins the Justice League just in time to help prevent an alien invasion. The League is struggling against a technologically advanced alien race, and Batman's strategic mind is the key to formulating a plan. He uses his resources and knowledge of Earth - based technology to create counter - measures against the alien weapons. Along the way, he forms bonds with his new teammates, especially with Wonder Woman, who respects his tenacity and intelligence. This experience makes him more integrated into the Justice League and changes his perspective on the larger scope of protecting the world.
One popular storyline could be a time - travel adventure. Imagine Batman Beyond getting accidentally sent back in time to the era of the original Justice League. He has to team up with the younger versions of the heroes to stop a threat that could change the future. For example, a villain from his time could have followed him back and is now trying to rewrite history to gain ultimate power.
One interesting storyline could be the Justice League having to deal with a mind - controlled Batman. Maybe some villain manages to take over Batman's mind, and the League has to figure out how to stop him without harming their friend. It would be full of action as they try to outwit Batman's strategic plans while also trying to break the mind control.
A third possible storyline could be a story of misunderstanding at first. The two groups could initially see each other as threats. For instance, the Justice League might mistake the Z - fighters' high power levels as a sign of aggression. However, through a series of events and battles, they come to realize that they are on the same side and must work together to face greater threats. This could involve some epic one - on - one battles between characters like Vegeta and Superman before they finally team up.
In the Justice League Dark and Batman story, one main storyline often involves the exploration of dark magic and the supernatural. Batman, being a detective, tries to understand and combat these otherworldly threats using his wits. Another aspect could be the interaction between the members of Justice League Dark, like Zatanna and Constantine, and Batman, as they have different approaches to dealing with the dark forces.
One possible storyline could be Kid Batman trying to prove himself to the full - fledged Justice League members. He might be given a small mission that seems simple but turns out to be full of unexpected challenges, like dealing with a new villain who has powers that can nullify the League's usual tactics. Another could be Kid Batman forming an unlikely alliance with a less - known member of the Justice League, and together they uncover a conspiracy within the League itself. Maybe there's a story where Kid Batman has to use his wits to save the day when all the other members are incapacitated.
One interesting storyline could be them teaming up to solve a mystery that involves both Gotham and Themyscira. Maybe a powerful ancient artifact has been stolen from Themyscira and is being used to create chaos in Gotham. Batman's detective skills and Wonder Woman's knowledge of the artifact's origin would make for an exciting adventure.