Because I have no idea...

"Fanfiction" is when a fan makes a fictional story wrote by themselves featuring characters from a video game or movie or anything series. I'm assuming you asked this because of how people say the plot to this game is like a fanfiction?

Fanfictions are stories that people write using characters/settings/worlds, etc. that were made up by someone else.

Like say I write a story where...Eggman collapses and dies of cholesterol poisoning before he throws the last Chaos Emerald into the Eclipse Cannon. The Colony Drop is averted and everyone goes home happy. Except for Shadow, who remains emo and kills himself.

This reminds me that GameTrailers commented on the 2006 Sonic the Hedgehog's plot elements to be "pretty ridiculous stuff", and that "You might actually be better off reading Internet fanfiction." Here's the link:

http://www.gametrailers.com/player/15248.html