Some ideas for Castle in the Sky fanfiction include a time - travel concept. What if someone from the modern world traveled back to the time of Laputa? They could introduce new ideas and technologies that change the course of events. Another idea is to have a story centered around the magic crystals. Maybe there are more crystals hidden in other parts of the world and Sheeta and Pazu go on a new adventure to find them. And a fanfic about a character who was born on Laputa but got lost in the outside world and is trying to find their way back home could also be great.
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.
Maybe Castle's pregnancy is part of a prophecy in the fanfiction world. Beckett, being the skeptic, has to come to terms with this strange turn of events. The two of them then embark on a journey to figure out what the prophecy means for their future and the future of their unborn child. This would involve a lot of mystery and exploration.
One idea could be that Brennan and Castle team up to solve a crime that has elements related to both their areas of expertise. Maybe it involves a historical skeleton discovery at a crime scene Castle is investigating.
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.