A plot could involve Terry partnering with some of the few remaining 'good' characters in the Injustice world like Green Arrow. They could form an underground resistance against the tyrannical regime. Terry's advanced technology from his time could give them an edge in their fight, like using his cloaking device to avoid detection during their missions.
Perhaps a fanfiction could focus on the psychological impact on Terry when he enters the Injustice universe. He's used to a different kind of crime - fighting street - level villains in his Gotham. But here, he's facing heroes gone bad. He could struggle with the decision of whether to use lethal force against them, which is something he's not accustomed to in his own universe.
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 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 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.
Perhaps they could start off as rivals in the fanfiction. Batman from the present is skeptical of Batman Beyond's more high - tech approach. But as the story progresses, they learn from each other and become a great team. For example, Batman could teach Batman Beyond some of his old - school detective skills, while Batman Beyond shows Batman new ways to use technology in combat and surveillance.
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.
Another plot could involve a character from the original Cadmus in the Batman Beyond timeline. For example, a revived clone or an old scientist who has new plans. They could be using the advanced technology of the future to bring back old threats or create new ones. Batman Beyond would have to use his unique skills and gadgets to deal with this. He might also team up with some of the new heroes in the future Gotham to take on Cadmus.
A great plot could involve Nightwing training a new generation of heroes in the 'Batman Beyond' universe. He could share his old - school combat techniques with the more tech - reliant heroes, leading to some interesting clashes and growth. For example, he might have a hard time getting used to the new gadgets while the younger heroes struggle with his more hands - on combat style. And together they have to face a villain who is exploiting their differences.
One idea could be exploring a new villain in Neo - Gotham. Maybe a tech - based criminal who can hack into the Bat - suit's systems, creating a whole new set of challenges for Terry McGinnis. Another could be a story where Terry has to team up with an old - school Batman villain who has somehow resurfaced in the future, like the Riddler, but with a new high - tech twist on his riddles.
Maybe the twins are new villains in Gotham. They have unique powers that they use to challenge Batman Beyond. For example, one has the power of illusion and the other has super strength. Their combined efforts make them a tough foe for Batman to face.
One idea could be to explore a future where Batman Beyond has to face an old enemy from the original Batman's time that has been resurrected with new, advanced technology. This would create a clash of old and new styles of combat and detective work.