Well, a common plot point could be that an outside force or person forces them to keep up the pretense. Maybe it's someone from Castle's past, like an old acquaintance who has some sort of vendetta against him. This person could be using Beckett as a way to get to Castle. So Beckett and Castle have no choice but to pretend to be separated to protect themselves and those around them. This would add a layer of danger and mystery to the fanfic, as they try to figure out how to deal with this threat while also keeping their pretend separation believable.
In a fanfic like this, there could be a lot of emotional turmoil. Beckett and Castle might start to realize how much they actually rely on each other. When they are pretending to be separated, they could find that they miss the little things about each other. For instance, Castle might miss how Beckett always has a smart comeback during their banter, and Beckett might miss Castle's goofy sense of humor. This could lead to some internal conflict for them as they try to maintain the facade while also dealing with their growing feelings for each other during this 'pretend' separation.
Another thing that could occur is that Castle decides to confront Beckett about what he saw. He could be really straightforward and ask her what's going on between her and Vaughn. This could lead to an argument or a really honest conversation about their relationship.
Perhaps they are trying to protect their relationship from outside interference. For example, if there are people in Castle's publishing world or Beckett's police department who don't approve of their relationship, they could pretend to be separated to avoid any negative consequences. This would allow them to still be together in private while keeping up the appearance of being single in public. Also, it could be a way to test their relationship. They might want to see how they would fare on their own and if their feelings for each other are strong enough to withstand a period of 'separation'.
One possibility is that they would face some challenges right after getting married. For example, they might have to deal with combining their two very different lifestyles. Castle is used to his flamboyant and sometimes chaotic writer life, while Beckett has a more structured detective routine. But through communication and love, they would find a way to make it work.
One possibility is that Castle has booked the hotel for a romantic getaway by himself, and seeing Beckett there completely throws him off. Beckett could be there for a much more serious reason, like following a lead on a dangerous criminal. Castle may start to worry about Beckett's safety and decides to stay close to her. As they interact more within the hotel, they might realize how much they've missed each other's company, and this chance meeting could be the start of something new between them, whether it's a new level of friendship or a re - awakening of their romantic feelings.
A Castle and Beckett baby fanfic could be about their journey into parenthood. It might explore how they adjust to having a baby in their lives. For example, Castle could be super excited and start writing new stories inspired by his new family experience, while Beckett might be a bit more cautious and protective.
They'll become even closer. The knowledge of a new life will bring them together on a deeper level. There'll be more tenderness between them.
There could be. The Castle fandom is quite creative, and a pregnancy plot for Beckett is a popular trope in fanfiction. Some fanfics might focus on the romantic aspect of it, with Castle being over - the - moon and taking extra care of Beckett. Others might explore the more practical and challenging sides, such as Beckett still trying to solve cases while dealing with pregnancy symptoms.
In a fanfic where they have a baby, their relationship would shift. They would now be partners not only in crime - solving but also in parenting. Castle would likely become more domesticated, helping with diaper changes and midnight feedings. Beckett would have to learn to let Castle in more on the parenting front, and they would communicate more about family - related matters. This new aspect of their relationship would add a different layer of complexity and closeness to their bond.
He could react with anger. After all, if he has feelings for Beckett, seeing her with someone else like Vaughn might make him furious. He might lash out at both Beckett and Vaughn without really understanding the situation.
In this fanfiction, the baby boy could be the center of a family drama. Maybe Castle's ex - wife shows up, claiming she has some rights to the baby. This causes a rift between Castle and Beckett as they deal with the legal and emotional turmoil. However, in the end, they come together stronger than ever, with their baby boy being the glue that holds their family together.