Another storyline might involve Beckett having a unique connection with his potential donor. Maybe the donor is someone he has met briefly before, and as he awaits the transplant, he has dreams or premonitions about this person. This could add an element of mystery and hope to the fanfic.
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.
One possible storyline could be that Castle goes into a deep depression. He might isolate himself from his friends and family, constantly reminiscing about their time together. He could also become obsessed with finding out the truth behind her 'death', suspecting foul play and starting his own investigation, even if the official version says it was an accident.
I'm not sure specifically as I haven't read that particular fanfic. But generally, it might be about a castle that somehow needs a transplant, perhaps in a magical or fictional context. It could be about restoring the castle in some way, like transplanting parts of it from another location or time.
A great one is about a young boy. He had a rare liver disease. After the transplant, he bounced back quickly. He is now able to go to school and play with his friends like any other normal kid.
One story could be about a person who regained their energy and was able to travel again. After the liver transplant, they no longer felt constantly fatigued. They started small, with local trips, and then gradually worked up to international vacations, seeing places they had always dreamed of.
One possible plot could be that Beckett is kidnapped by a rival group who wants to use his skills or knowledge for their own gain. His friends then embark on a dangerous rescue mission.
One possible plot could be Beckett's intense search for the abducted child. She might use her detective skills to follow leads, question suspects, and piece together the mystery of the abduction. Another plot could involve the emotional journey of the people related to the abducted child, like the parents, and how Beckett interacts with them during the investigation.
Well, it could be that Beckett's mystery illness is actually a curse. In the fanfic, there might be a magical or supernatural element. For example, an old family feud with a witch or a wizard who put a curse on Beckett, and the story could revolve around breaking the curse to cure the illness.
It could also be a fanfic that takes place in an alternate universe. In this universe, the events of 4x23 didn't happen as they did in the show. Maybe Beckett didn't become a detective in the same way, and Castle meets her in a completely different situation. They then start to solve mysteries together in this new setting.
There was a patient named Mary. She had a liver transplant due to a genetic liver disorder. The operation was a great success. Not only did her liver function return to normal, but she also started to participate in light physical activities like walking in the park. The post - transplant care and the skill of the medical team played important roles in her success story.