Fever, light headache to migraine, stomachache, and back aches are the first symptoms. Usually the victim is a fanfiction author (hence the name) but it can effect fiction writers, poets, songwriters and essayists as well. The fever and migraine is usually the direct cause of the disease.
After that, the victim usually watch, reads or writes something. The victim gets attracted to a certain character, either the personality or looks, sometimes both. Then the victim goes through hallucinations and becomes obsessed with this character. In the first few days this will be very powerful, and it's advised to not bring up this character to the victim. Speaking ill of him or her can lead to aggressiveness and the victim will take the insult against their character.
Some will grow out of the aggressiveness, while others never do.
But the disease itself is incurable. No matter how mild, the victim will still squeal in delight or go into hallucinations whenever he/she sees something which can relate to the character which was the cause of the disease.
In a few rare cases, the victim will have two characters or more which makes them go into these hallucinations.
The challenge for you is to guess what made me go into one this time by looking on the picture. Fic to the first person who gets the connection and names the character and which series he/she is from (no, it's not really ElfQuest related.)