There are basically three kinds of fan novels: fans of anime/games, fans of novels/movies and fans of history/real people.
The first one is common.
The characters borrowed from the original works are even novels written with world outlook, such as Romance of the Three Kingdoms, which is fan fiction in the history of the Three Kingdoms. Such a serious subject is rare in fan fiction.
In today's fan fiction, men usually prefer to love women, especially women.
There are basically three kinds of fan stories: completely supplementing the story with the original world view, spoofing with the original characters, and describing their feelings with the original characters. The last one is common.
Form of works
1, completely original interpretation, that is, comics, movies or other text versions.
2. Emotional analysis of the original characters.
3. Other plots of the original characters' development.
4. Other stories of the original characters in different time and space backgrounds.
5. Interpretation of original fairy tales.
6. Other types.
It can be seen that this special form of work is basically attached to the original work, which has a fundamental decisive role in the expression of its content and the attitude of readers and authors towards it.