Well, you could have a plot where a strange epidemic hits Gotham that affects people's minds and makes them act in erratic and dangerous ways. The Dark Knights would have to find the source of this epidemic while also trying to keep the city from descending into total chaos. Or perhaps a story in which a powerful and mysterious figure from another dimension arrives in Gotham and challenges the Dark Knights, testing their limits and forcing them to adapt to new and unknown powers.
A great plot could involve the Dark Knights having to team up with some of Gotham's most unlikely allies, such as former villains who have turned over a new leaf. They could be brought together by a common threat that is too big for any of them to handle alone. Also, a plot where the Dark Knights discover a long - hidden secret about Gotham's founding that has the potential to change everything they know about the city and their role in it.
One idea could be exploring the backstories of the Gotham Knights more in - depth. For example, you could write about how they trained before becoming the Knights. Another idea is to create new villains for them to face. Maybe a villain with the power to manipulate technology in Gotham. Also, a fanfiction could focus on the relationships between the Knights, like how they handle disagreements within the team.
Perhaps the Dark Knights could be on a quest to find a long - lost artifact that would give them ultimate power. Along the way, they face challenges from various Middle - earth races who oppose their goal. This could lead to epic battles and unexpected alliances. For example, they might encounter elves who are protecting the location of the artifact, and a complex power struggle ensues.
The Joker is a character that can't be ignored. His chaos - loving nature and his long - standing enmity with Batman would make for great drama in the fanfiction. Then there's Commissioner Gordon. He represents the law in Gotham and his partnership with the Dark Knights, especially Batman, is crucial. Also, Nightwing, who was once Robin and has his own set of skills and a different way of operating in Gotham compared to Batman.
A great plot for Gotham Academy fanfiction could be a story centered around a school competition that turns out to be rigged. The main characters suspect foul play and start their own investigation. Or perhaps a story where a character from a villain's family enrolls at the academy and has to deal with the prejudice from other students while also trying to prove they're not like their family. Also, a plot about a haunted dormitory at Gotham Academy would be really cool. The students would have to figure out the mystery behind the hauntings.
A great plot could be that the male OC is a street magician in Gotham. One day, he discovers that his magic tricks are actually real magic due to an ancient artifact he found. He then uses this magic to fight crime, but he has to keep it a secret from the authorities and the criminal underworld. Or perhaps the male OC is a detective who has a unique ability to see the memories of the dead. This helps him solve crimes that no one else can, but it also takes a toll on his mental health as he is constantly exposed to the trauma of the victims. Another plot could be that he's a young heir to a wealthy family who decides to use his family's resources to fight against the poverty and crime in Gotham instead of living a life of luxury.
Perhaps there's a villain in Gotham who has discovered a way to siphon the Flash's speed force. The Flash has to go to Gotham to stop this villain, and in the process, he meets the various characters of Gotham like Gordon and Catwoman. They all have to work together to not only stop the villain from stealing the speed force but also from using it for some evil plan in Gotham.
Maybe there's a meta - human or a super - villain who is causing chaos in both cities. Batman is too occupied with Gotham's internal affairs, so Arrow comes to help. They discover that the villain has a base in an abandoned area between the two cities. They have to combine their resources, like Arrow's high - tech arrows and Batman's detective skills (even if Batman himself isn't directly involved but his influence on Gotham's crime - fighting is there), to take down the bad guy.
One idea could be Marinette moving to Gotham and using her unique skills to help the city in a different way than the local heroes. For example, she could use her fashion design skills to create protective gear for the people in dangerous areas. Another plot could involve her befriending some of the Gotham characters like Barbara Gordon and sharing her positive outlook, which gradually changes the gloomy atmosphere of Gotham. She might also get involved in some of the city's mysteries and use her cleverness to solve them.
One idea could be exploring the backstories of the Tenkai Knights more in - depth. For example, how they got their powers and what their lives were like before becoming knights. Another could be a crossover with another similar - themed anime, like creating a scenario where the Tenkai Knights have to team up with characters from another mecha - based show to fight a common enemy. And a third idea is to focus on the relationships between the knights and how they grow and develop over time.
A plot could involve Merlin getting cursed and the knights having to find a way to break it without Merlin's magic to guide them. They might have to rely on old legends and their own wits to save him. This could lead to some great character development for the knights as they face challenges they usually rely on Merlin to solve.