How many different kinds of fanfic are there? I'm not really sure - here are some incomplete thoughts on the subject:
- Emotional Projection (Fluff/Dark): The story tries to create certain emotions in the reader. Lots of romances fall into this category.
- Character Investigation: Trying to completely flesh out a character by investigating & proposing reasons for their actions - making the character "complete" in a sense.
- Character Exploitation: These are the ideas that start: "Wouldn't it be cool is {X character} did/went through/etc." The purpose is to put the character into truly weird situations (e.g. MLC) to see how they react.
- Character-Driven: Related to character investigation, but the focus is on how the character changes the world around themselves - and the consequences of that.
- World Investigation: The character is used as a proxy to develop the world (makes sense for fantasy). I'd say that most world-investigation stories are very related to character-driven or even character exploitation stories, in that they need a drive to move the character through the world.
What else is there?
See, I was trying to classify this story summary on FF.net: "When the Dursleys are killed, Harry is left without legal guardians and is left prey to an ancient law that would see him owned by those who wish him harm. For his protection, he marries Severus and his new life begins. Marriage fic format but with a plot."
I'm not sure how to describe it....
(Also, how is a minor who needs guardians eligible for marriage?)