Well, if they were always married in fanfiction, we might see them grow as a couple in unexpected ways. There could be storylines about starting a family or dealing with long-term relationship issues in a more committed context.
It could lead to a completely different story arc with new challenges and developments for the couple.
Some fanfictions might also explore the medical aspects in a more historical or fantasy context if the castle setting implies a different time period or a magical world. For instance, if it's a medieval - like castle, they might describe the midwives and their methods, or if it's a magical castle, there could be some special care related to the baby having potential magical powers.
There probably are. Fanfiction is a great way for fans to expand on the storylines they love. In the case of Castle, the relationship between Castle and Beckett was a big part of the show. A pregnancy storyline for Beckett could add a whole new layer of drama and character development. You might have to do some searching through different tags on fanfic sites to find ones specifically about Beckett being pregnant.
A good 'castle married fanfiction' often has well - developed characters. Since we already know Castle and Beckett from the show, in the fic, they should still retain their core personalities. For instance, Castle's charm and Beckett's determination.
A good Tony and Kate married fanfiction could also delve into their emotional connection. Like how they support each other through tough times. Maybe one of them has a family issue or a problem at work that the other helps them get through. It could show their growth as individuals and as a couple. It could also include some sweet moments like anniversaries or surprise dates that they plan for each other.
I'm not sure specifically as there could be many different interpretations. It might be a fan - created story where a character named Castle believes that Kate is cheating in the context of their relationship within the fan - created scenario.
One possible plot is that Kate is in danger during an undercover operation. Castle, using his connections, gets wind of it and races to the scene. He manages to get her out just in time.
I'm not sure specifically as there could be many different fanfics with that title. It might be about a character named Castle who has a strong belief that Kate is alive. Maybe Kate was in some sort of dangerous situation or presumed dead, and Castle is determined to prove she's alive.
One great story could be about their baby's first steps. Imagine Castle being overly excited and Beckett trying to be the calm one but also bursting with pride. The baby might stumble towards Castle's study, where all his books are, as if drawn to the world of stories just like its father.
Perhaps in the fanfiction, Kate's pregnancy was a big surprise to everyone. When she's giving birth to this 'big baby', Castle is by her side, reminiscing about their journey together. The plot could involve the medical team being astonished by the size of the baby and how they handle the situation. It might also show how Kate and Castle prepare for the new addition to their family in the days following the birth.