One idea could be exploring Batman's initial reaction to being part of the Justice League in a 'Batman Begins' context. Maybe he's hesitant at first, still haunted by his past traumas from 'Batman Begins' and having to learn to trust these super - powered beings. He could be constantly assessing the League's motives and methods, which could lead to some internal conflicts within the team.
A possible plot could involve the villains from 'Batman Begins' somehow being connected to a greater threat that requires the Justice League's intervention. For example, Ra's al Ghul's League of Shadows might have a secret alliance with an alien force that the Justice League discovers. Batman would then have to balance his personal vendetta against Ra's al Ghul and his newfound responsibility to the League.
One idea could be a story where Batman has to lead the Justice League in a fight against a new, powerful and mysterious villain that can manipulate time. Another could be a fanfiction exploring the relationships within the Justice League when they are stranded on an uninhabited planet and have to rely on each other more than ever.
A possible plot idea is that Batman discovers a dark secret within the Justice League that they are unaware of. This secret could be something that could potentially destroy the League or change their moral compass. Batman then has to decide whether to confront the League directly or try to fix the problem on his own, which causes the 'vs' situation as the League may see his actions as a threat.
One interesting plot could be Batman's distrust of the Justice League's unrestrained power leading to a full - on confrontation. He might secretly plan to take down each member one by one, using his intellect and prep time. Another could be the Justice League being mind - controlled and Batman having to fight them to break the control.
One idea could be a time - traveling adventure. Batman Beyond gets sent back in time to the era of the original Justice League. He has to team up with them to stop a threat that was once thought defeated but has returned in a new form. The contrast between the high - tech world of Batman Beyond and the more classic superhero settings of the original Justice League would create interesting dynamics.
A cool concept could be a 'Batman Justice League fanfiction' set in an alternate universe where the League is formed much earlier in history. Batman has to adapt to working with heroes from different time periods and cultures, and they all have to figure out how to use their powers in a world that's not as technologically advanced as their own.
One idea could be a story where Batman has to lead the Justice League in a fight against a powerful new villain who can manipulate time. This would put Batman's strategic skills to the ultimate test as he tries to coordinate the different powers of the League members. Another plot could be that a member of the Justice League is secretly under mind control and Batman has to figure out who it is before they cause too much damage.
Perhaps the Justice League watches 'Batman Begins' as part of a team - building exercise. But as they watch, they realize that Batman's more brutal and unforgiving tactics at the start make them question if they should be more like him in dealing with certain villains. For example, Superman might wonder if he should be less lenient with Lex Luthor. This could lead to internal debates within the League.
One idea could be that Batman discovers a hidden weakness in an enemy that's about to destroy the Justice League. He uses his detective skills to find a way to counter it and saves them at the last minute. For example, if the enemy has a device that can nullify the League's powers, Batman figures out how to disable the device.
A plot could revolve around a time when Batman is framed for a crime within the superhero community, and Wonder Woman is the only one who believes in his innocence. They work together to clear his name, all while uncovering a conspiracy within the Justice League itself. This would explore their trust in each other and their individual approaches to solving problems.
One idea could be a story where Batman has to lead the Justice League in a fight against a new, powerful villain who can manipulate time. The League members start losing their memories one by one, and Batman has to figure out a way to stop the villain while also restoring his team's memories.