Which is your favourite Headcanon or Fan-theory, even if it has been officially disproved?
Mine is from Final Fantasy VIII, the theory is the final antagonist is actually the main female protagonist from the future. There are many points supporting this theory, and they make more sense than one Square official telling that it's not true.
This article has everything you need to know about this theory: http://www.heartilly.com/rinoa/article_ultimecia.html