Maybe in the fanfiction, there's an alternate universe where Batman is a father figure to a young sidekick who is still in diapers. The story could revolve around Batman teaching the kid about justice and heroism while also taking care of the diaper - changing duties.
Another plot could be that a villain has cursed Batman to be in a diaper - like state as a form of humiliation. Batman then has to find a way to break the curse while facing the challenges of being in this rather embarrassing situation, all the while trying to keep Gotham safe.
One idea could be exploring what if Bruce Wayne's identity as Batman was exposed accidentally by a new high - tech surveillance system in Gotham. Another could be a story where Batman has to take on a new identity temporarily to infiltrate a secret criminal organization that has been studying his every move as Batman.
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.
A possible plot could be that an evil organization creates a special diaper for Mewtwo which is actually a mind - control device. Mewtwo has to struggle against the control while trying to figure out how to remove the diaper. Or perhaps Mewtwo discovers a group of baby Pokemon who are being mistreated because they are always in dirty diapers. Mewtwo uses its powers to clean and care for them, and in the process, learns about the value of kindness and nurturing.
Well, perhaps in a fanfiction, a young wizard accidentally casts a spell on himself that makes him lose all his potty - training knowledge. So he has to deal with wearing a diaper while still trying to attend Hogwarts classes. This could lead to some really awkward and funny moments, like when his friends discover his situation or when he has to quickly change during a Quidditch match.
A plot could involve a time - travel scenario where Batman and Supergirl are sent back in time to prevent a major event that would change the future of both their worlds. They would have to work together, using their different skills and knowledge of their respective eras.
One idea could be exploring the relationship between Batman and Robin in a more emotional depth. Maybe Robin is going through a tough time at school and Batman has to balance being a mentor and a crime - fighter. Another could be a time - travel plot where the Bat - family gets sent to different eras in Gotham's history and has to adapt and still fight crime.
One idea could be that Batman and Robocop team up to take on a powerful criminal organization that is using high - tech weaponry. They would combine Batman's stealth and detective skills with Robocop's firepower and law enforcement programming.
One idea could be Batman using his detective skills to uncover a hidden threat that the Avengers initially overlook. For example, he might notice some small, seemingly insignificant details during a battle scene that lead him to a much larger conspiracy.
One idea could be exploring the psychological state of Batman during Knightfall more in - depth. Maybe focus on his nightmares and how they affect his decisions in the story. Another could be a what - if scenario where a different character takes on the role of protecting Gotham during Knightfall, like Oracle guiding a team of young vigilantes.
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.