Obviously, Beckett would be one of the main characters. There might also be her partner, if she has one in the fanfic's storyline. Her doctor or medical team could also be main characters as they play important roles in dealing with the complicated pregnancy.
One common theme could be the emotional turmoil of the characters. In a complicated pregnancy, there's often a lot of fear, hope, and stress. Another theme might be the support system around the pregnant character, like how friends and family react. Also, the medical aspects could be a theme, such as dealing with difficult diagnoses and treatments during pregnancy.
Beckett is obviously one of the main characters as the one with the mystery illness. There might also be a doctor character who is determined to find out the cause of the illness and treat it.
Bernadette and Howard are also common focuses. Given their own relationship quirks and Howard's transformation from a womanizer to a family - man - in - training, a pregnancy can add more depth. Bernadette's pregnancy could show her taking charge even more in the relationship and family matters.
A coworker who has a crush on Beckett might be a main character. They could be the one who stays by Beckett's side the most during his recovery, and this could lead to a romantic sub - plot.
Obviously, Beckett and his daughter are the main characters. Beckett is likely to be a protective figure, using his skills and knowledge to try and get them out of the trapped situation. His daughter, on the other hand, might be the source of hope or inspiration in the story, perhaps with her own unique ideas to contribute to their escape.
Obviously, Beckett would be the main character. But there could also be a hotel concierge who plays an important role. The concierge could be someone who is either very helpful to Beckett, guiding him around the hotel and the local area, or someone who is a bit of a troublemaker, causing difficulties for Beckett during his stay.
The main characters are obviously Beckett and Josh. Beckett seems to be a character who is involved in some sort of relationship that they are about to betray through cheating with Josh.
The main characters would be Beckett and Castle, as the title implies. Beckett is likely to be the one taking some sort of action in relation to Castle.
The parents of the Beckett baby would surely be main characters. They would be in a state of panic and desperation, driving the story forward with their search for their child.
His doctor could be a main character. The doctor could be portrayed as a very dedicated and empathetic person, constantly providing Beckett with hope and medical advice. For instance, the doctor might have to break some tough news to Beckett about the risks of the transplant, but also encourage him to stay positive.