One idea could be exploring the backstories of the characters in the Dark Castle. For example, what led them to be in the castle in the first place. Another could be creating a new adventure within the castle, like finding a hidden chamber with ancient secrets. Maybe also a fanfiction about a character from the outside world getting trapped in the Dark Castle and trying to find a way out.
Well, you could write a fanfiction where the Dark Castle has a mind of its own. It could be playing tricks on the characters, leading them into false passages or showing them illusions. Or perhaps a story about the relationships between different creatures in the castle, how they interact, cooperate or compete. Also, a time - travel themed fanfiction where a character goes back in time to the origin of the Dark Castle would be quite interesting.
One idea could be to have the characters from Firefly somehow land near the castle. Maybe they are in need of supplies and the castle inhabitants initially view them as a threat. Then, through a series of events, they start to work together, with the Firefly crew sharing their space - traveling knowledge and the castle people providing shelter and local resources.
Maybe the rocket man has to rescue someone trapped in the castle. The castle could be filled with various obstacles and enemies. He uses his rocket - related skills to overcome them all.
Well, perhaps in the 'Naruto Castle of Glass Fanfiction', the Castle of Glass is actually a creation of an old and forgotten clan. Naruto and his team could be on a mission to find out more about this clan and the purpose of the castle. They might encounter various traps and puzzles inside the castle. And as they progress, they learn that the castle has a connection to Naruto's own family history, which adds an extra layer of mystery and importance to the whole adventure.
A great fanfiction idea related to 'Castle of Black Iron' might be to create a prequel. Show how the castle was built, who were the original inhabitants, and what events led to its current state. You could also do a crossover with another similar fantasy world. Maybe some characters from 'Castle of Black Iron' end up in a different magical realm and have to adapt. Or, you could write a story from the perspective of the villains in the 'Castle of Black Iron', explaining their motives and how they view the world.
One idea could be a story where Hogwarts Castle itself becomes sentient and starts to communicate with the students. It could offer hidden secrets and magical powers to those who can understand it. Another could be a fanfiction where Harry discovers a hidden chamber within the castle that leads to an alternate magical world.
A cute plot could be that their baby is born during a big case. Castle is away when Beckett goes into labor, and he has to race back. When he finally arrives at the hospital, he is just in time to hold their new - born, and they both realize how their lives are about to change in the most wonderful way.
One idea could be that the baby in the castle has some special powers. For example, it can communicate with the castle's spirits. Another could be a story where the baby is a lost heir to the castle's throne and there are various characters trying to protect or use the baby for their own gain.
Well, you could focus on the relationships between the characters in Dark Cloud. Like writing a fanfic about how Goro and Ungaga became friends. Or you could take the setting of the game and expand on it. Suppose there are other hidden areas in the Dark Cloud world that the main characters haven't discovered yet. Write about their adventures in those areas.
One idea could be to explore the darker side of the PPGZ characters' powers. For example, Blossom's leadership could turn into a controlling dictatorship within the group. Another could be a scenario where the villains manage to corrupt the girls, making them fight against the very people they once protected. Maybe a new, extremely powerful villain emerges who uses mind - control on the PPGZ, leading them to do his bidding in a very dark and twisted way.
Some dark zootopia fanfiction might also focus on the psychological toll of living in a society that seems so perfect on the surface but has hidden problems. Characters could struggle with depression or anxiety, like Judy Hopps realizing that her dream job isn't all she thought it would be and having to deal with the corruption and darkness she discovers within the Zootopia Police Department.