One plot could be that Batman is injured while exploring an ancient, dangerous alien artifact as part of a Justice League mission. His injury has some strange side - effects that start to affect his mind. The other Justice League members must not only deal with the external threats that the artifact may pose but also figure out how to save Batman from the internal turmoil his injury has caused. This could lead to some deep character exploration and development for all the members.
A plot idea could be that Batman is injured by a kryptonite - enhanced weapon during a fight against a Lex Luthor - controlled Superman in the Justice League. His injury makes the other members realize how vulnerable they are without Batman's strategic mind. So they have to find a way to heal him quickly while also preventing Luthor from causing more chaos.
In some fanfictions, Batman might be injured while investigating a dangerous conspiracy. He gets too close to the truth and the people behind it try to eliminate him. They set up traps, like a high - tech booby - trapped building. Batman is caught in an explosion or a collapsing structure, which results in his injury. Then the Justice League has to come to his rescue and deal with the conspiracy.
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.
One possible scenario in such a fanfiction could be that Batman gets injured during a battle with a powerful new villain in the Justice League. Maybe he's trying to protect a civilian and takes a direct hit that leaves him severely wounded. His fellow Justice League members then have to figure out how to continue the fight while also taking care of him.
In a fanfic where Batman is injured, it could lead to many interesting plot developments. Maybe the other Justice League members have to step up their game. Superman might take on a more protective role over Gotham in Batman's absence. Wonder Woman could be the one to lead the investigations that Batman usually handles. This kind of injury to Batman can create a shift in the power dynamics within the Justice League.
One plot idea could be that Batman discovers a hidden threat to the Justice League that even their superpowers can't detect easily. Maybe it's a new type of mind - controlling technology. He uses his detective skills to find the source and then devises a plan to free his teammates from its influence.
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 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.
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.