Lois Lane is a must - include. She can be the love interest and also a strong - willed journalist. Jimmy Olsen is also great, providing some comical relief and being Superman's friend. Lex Luthor is an obvious choice as the main villain, always plotting against Superman.
One idea could be having Superman face an enemy that can manipulate time, causing chaos in Metropolis. Another could be a story where he has to deal with a powerful alien artifact that is affecting his powers. Maybe also a plot where he teams up with a new superhero from another planet.
Clark would probably be initially shocked but then quickly regain his composure. He is used to facing difficult situations. He might start to assess his surroundings, looking for any weaknesses in the place where he is being held that he can use to his advantage.
Superman, of course, is the most important. Then there's Lois Lane, the journalist who is always on the hunt for a story and has a special relationship with Superman. Lex Luthor is also crucial as the main antagonist.
In the 'The Adventures of Superman Novel', a significant plotline is Superman's origin story. How he came from Krypton and was raised on Earth. His discovery of his powers and how he decides to use them for the greater good. Also, his relationships with Lois Lane and other characters in Metropolis play a big part in the plotlines as he tries to balance his personal life with his superhero duties.
Obviously, Superman himself is the most important. He is the hero with superpowers. And Lois Lane is also important as she is often in the middle of the stories and has a relationship with Superman.
One main theme could be heroism. Superman is always saving the day, which shows the importance of having heroes. Another might be justice as he fights against evil to bring fairness.
Some characters might be critical. If they have a strong sense of the 'canon' Superman, they could nitpick at the details in the fanfic that don't match up. For instance, if the fanfic changes Superman's origin story too much, they might frown upon it.
Their relationship might develop through shared experiences. For example, when they are both investigating a mystery in Metropolis. Clark uses his super - powers subtly to help Lois get to the bottom of the story, and in the process, they grow closer. As they face danger together, they start to rely on each other more and more, which deepens their connection.
One example could be a story where a female Clark fan uses her admiration for him to inspire others in Metropolis. She might start a movement of positive change, like promoting Clark's values of truth and justice on a grassroots level. This could involve her writing articles or giving speeches about the symbol that Superman represents.