It could start with a strange magical event that results in Lucy's pregnancy. Caspian is initially shocked but then becomes very protective. They decide to keep it a secret for a while. But as Lucy's condition becomes more obvious, they have to face the reactions of their court. Some may be happy, while others may be worried about the implications for the kingdom.
One idea could be that they discover the pregnancy during a time of peace in Narnia. They then face the challenges of preparing for a new life while also dealing with the expectations of their people. For example, Caspian might worry about how to protect his family in a world that still has some threats. Lucy, on the other hand, could be thinking about how to raise a child with the values of Narnia.
One plot idea could be that they are separated during a battle in Narnia. When they are reunited, the relief and joy lead to a passionate kiss. This kiss could symbolize their new - found determination to never be parted again and fight side by side.
One idea could be that the baby has a special power. For example, the baby might be able to communicate with magical creatures in a way that no one else can. This could lead to all sorts of adventures as Lucy and Caspian try to protect the baby from those who might want to use the power for evil.
Well, perhaps in the fanfiction, Lucy and Caspian are from different kingdoms that are at odds. But when they are sent as envoys to negotiate a peace treaty, they discover their mutual respect for nature and justice. They start to secretly meet and exchange ideas. As time passes, their feelings turn into love. They then have to struggle against the political forces that want to keep their kingdoms separate while trying to stay together.
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.
Maybe there could be a plot where an evil force in Narnia is trying to separate them. Lucy and Caspian have to go on a dangerous journey together to stop this force. Along the way, they rely on each other's strengths. Caspian protects Lucy from physical threats while Lucy uses her magic to solve various puzzles. Their bond grows stronger through these trials and they eventually confess their love.
Their relationship can develop through shared experiences. For example, they can attend prenatal check - ups together in a Narnian - style way. This would bring them closer as they anticipate the arrival of their baby.
One common theme is adventure. Given their backgrounds in the Narnia stories, fanfictions often send them on new quests. For example, they might explore uncharted parts of Narnia or other magical realms.
I'm not sure specifically if there is a fanfiction with Susan and Caspian where there is a pregnancy. There are a vast number of fanfictions out there, and it would depend on the creativity and direction of different authors. Some fanfictions might focus on adventure and relationship building between the two characters without including such a plot element, while others might explore more complex storylines that could involve pregnancy.
One idea could be that they discover the pregnancy unexpectedly. Maybe they were in the middle of a big adventure in their magical world and then Lucy starts showing signs. It throws them into a new set of challenges as they have to balance their duties in their guild with preparing for a new life.
In the fanfiction, after getting married, they may face challenges in terms of leadership. They need to make decisions together for the good of Narnia. But their different perspectives - Caspian's Narnian - born knowledge and Lucy's insights from her own world - might sometimes clash. Also, there could be external threats. Enemies might see their union as a weakness to exploit or a new power to fear. They would have to work hard to prove that their marriage strengthens Narnia rather than weakens it. And on a more personal level, they may struggle to find time for each other with all their royal duties.