Perhaps a story where Batman discovers a conspiracy within the Injustice League that involves mind - controlling the heroes. It could delve into his detective skills as he tries to uncover the truth and save his comrades. This would be full of mystery and action.
A fanfiction could focus on the emotional journey of Batman in the 'injustice for all' setting. How he copes with the moral dilemmas, like when he has to make tough choices between saving civilians and stopping supervillains. It could show his inner struggle and growth as a character, which is always an engaging aspect of Batman stories.
One interesting storyline could be a redemption arc for Superman. In the Injustice universe, Superman has gone down a dark path. A fanfiction might explore how Batman tries to bring back the good in him, with lots of emotional confrontations and moral debates between the two.
One idea could be exploring Batman's internal struggle in the Injustice universe more deeply. Maybe he has a nightmare where he becomes like the tyrannical Superman, and this makes him question his own actions and methods even more.
One interesting storyline could be a reimagining of Batman's first encounter with the Joker in the 1939 fanfiction context. Maybe the Joker starts as a small - time criminal and Batman has to figure out his true motives early on.
One idea could be that Batman tries to train Supergirl to better control her powers in the context of the Injustice 2 universe. He might see her as a potential force for good against the tyrannical regime. Another could be that Supergirl discovers a way to bring back the more heroic Superman she once knew, and Batman has to decide whether to trust her plan or not.
One idea could be exploring an alternate universe where Terry McGinnis (Batman Beyond) is pulled into the Injustice universe and has to deal with the morally compromised heroes. He might try to find a way to bring back the true sense of justice among them. For example, he could start by trying to reason with Superman, showing him the error of his ways through his own experiences in his own universe.
One interesting storyline could be Batman having to deal with a new villain who has the power to manipulate time while also trying to maintain his normal life as Bruce Wayne. This would add a whole new layer of complexity to his dual identity.
One idea could be that Batman and Wonder Woman have a major disagreement over how to deal with the Injustice regime. Batman wants to use more stealth and subterfuge while Wonder Woman believes in a more direct approach. This could lead to some intense battles between them, not physical but more of a battle of wits and ideologies.
One plot idea could be Batman trying to convince Wonder Woman to see the error of her ways in the Injustice universe. Maybe he shows her the long - term consequences of their actions on the common people. Another could be a story where Wonder Woman and Batman have to team up against a greater threat that makes them re - evaluate their stances in the Injustice conflict.
Batman himself is obviously very popular. He's the central figure and fans love to explore different aspects of his character in this 'injustice for all' scenario. His intelligence, combat skills, and unwavering sense of justice are always interesting to write about.
One interesting storyline could be a team - up against a powerful new villain that neither can defeat alone. They have to combine their unique skills, like Superman's super strength and Batman's detective skills.