A fanfiction could focus on Peter's return to Narnia during Prince Caspian's time. He could be a mentor to Caspian, teaching him about the old Narnia and how to better lead his people. They could also face a series of challenges together that test their leadership and friendship.
One idea could be a story where Peter and Caspian have to go on a secret mission together to find a lost magical artifact that can save Narnia from a new threat. They start off not getting along but gradually learn to respect each other's skills.
One idea could be that Peter gets lost in the forest of Narnia on his own during a quest and has to rely on his wits and some unexpected help from a minor character in the Prince Caspian story to find his way back to the main group. Another could be a time - travel twist where Peter is sent back to a crucial moment in Prince Caspian's past and has to figure out how to change things without disrupting the future of Narnia too much. And perhaps a story where Peter and Prince Caspian have a misunderstanding that leads to a mini - adventure to resolve their differences and strengthen their bond.
Some fanfictions also pair Lucy with Caspian. Lucy has her own unique magic and kindness, and when paired with Caspian, it can create interesting relationships, like her helping Caspian understand the more magical aspects of Narnia.
A great plot could be a time - travel related one. Maybe something goes wrong in Narnia, and Peter and Caspian are sent back in time to the very beginning of Narnia's creation. They have to figure out how to get back to their own time while also making sure that the events that led to Narnia's creation still happen as they should. They meet all kinds of ancient beings and learn secrets about Narnia that no one else knows.
One idea could be that Susan returns to Narnia in a time of great need, and she and Prince Caspian have to work together to defeat a new, powerful enemy. Maybe they discover an ancient magic that only they can unlock through their combined efforts.
One idea could be that Lucy discovers a hidden magical ability that helps Prince Caspian in a crucial battle. For example, she might be able to communicate with the spirits of the forest in a way that no one else can, and these spirits provide strategic advice to defeat an enemy. Another plot could involve Lucy getting lost in a mysterious part of Narnia and Prince Caspian embarking on a quest to find her, during which they both learn more about each other's pasts and grow closer.
One plot idea could be that Fem Harry Potter somehow gets transported to the world of Narnia during the time of Prince Caspian. She could use her magic skills, learned from Hogwarts, to help Caspian in his battles. For example, she might use spells like Protego to shield his army from enemy attacks.
Some fanfictions focus on the relationship between Peter and Caspian when they first meet. It could explore how they initially view each other with suspicion, being from different worlds in a way. But as they start to understand each other's motives and the importance of their roles in Narnia, they form a strong bond that helps them protect Narnia from various threats.
There might be a fanfiction where Peter Pevensie attends a magical school similar to Hogwarts but with Narnian elements. He could befriend students from different magical realms and they all go on quests together within the school grounds. It would be a great blend of the Narnia universe and the concept of a school - based magical adventure.
There might be a fanfiction where Lucy and Peter go back in time to the very beginning of Narnia. They witness the creation of the magical world and play a role in ensuring its future. In this story, they could interact with the great lion Aslan in a whole new way, perhaps learning secrets about Narnia's origin that no one else knows.
One interesting 'Prince Caspian' fanfiction could be about Caspian's adventures before he met the Pevensies. Maybe it details his training as a prince and how he learned about Narnia's secrets.