One popular theme is Komi-san's attempts at making more friends. Another could be Komi-san's experiences in different social situations outside of school. Also, fanfics might focus on the relationship between Komi-san and Tadano developing further in various scenarios.
The light - hearted and often humorous stories. For example, the way her classmates try to understand her and the comical situations that arise from miscommunications. It also has a great art style in the novel illustrations that enhance the overall appeal.