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.
I'm not sure specifically as I haven't read this novel directly. But generally, in the isekai genre, it might be about a second summoning to another world. Maybe the protagonist has been summoned once before and now experiences a second summoning with new challenges, adventures, and character development.